Criteria for the Acceptability of Scientific Theories as Locus theologicus: A Methodological Analysis of Catholic Church’s Reactions to the Cases of Galileo and Darwin (Bellarmine—Pius XII—John Paul II)

Abstract

The categories of demonstration and hypothesis appear constantly in the texts of Catholic theologians confronted with the new science of Copernicus and Darwin. They were used by Robert Bellarmine to reject Galileo’s scientific and realistic interpretation of Copernican theory. They were equally used by some neo-scholastic theologians against Darwin’s theory of evolution and reappeared in the official texts of Pope Pius XII and John Paul II. My paper will analyze these selected historical texts to show whether and how the epistemology and methodology adopted by their authors determined their acceptance or rejection of scientific theories as potential Loci theologici. Moreover, the historical-comparative approach should reveal in this theological tradition, for all its officially declared continuity, the progressive evolution of views on the meaning and role of demonstration and hypothesis in science, as well as official Catholic theology’s dependence on the historically changing notion of science and its method. This will allow me to discuss the idea of a changing scientific methodology as another very specific locus theologicus, this time metatheoretical. I will propose the idea of a non-absolute autonomy or relative dependence of theology on available meta-scientific solutions.

1. Introduction

Much has been written about the cases of Galileo and Darwin and the reaction of the Catholic Church. Several aspects of these issues have already been examined, including methodological and epistemological aspects, which will be addressed in this paper. However, the situation is different in the two cases. In the case of Galileo, a number of studies focus not only on the problem of Galileo’s method (as in Wallace 1988a, 1988b, 1995), but also on the problem of its relationship to the philosophical method accepted by the Church authorities of his time, especially Bellarmine, in the context of the interpretation of the Scripture (cf. McMullin [1967] 1988, 1998, 2013; Ashworth 1986; Baldini 1992; Coyne and Baldini 1985; Moss 1985). And it is this last question that is most relevant to the present study.

In the case of Darwin, there are several studies on his method (cf. Ayala 2009, pp. 10038f., and especially refs. 27–34; Ruse 1975; Thagard 1977; Warner 2009; Pence 2018, 2021–2022) and numerous studies on evolution and Christian thought (cf. Brooke 1991) and his bibliographic essay; Dupree 1986; Gregory 1986). One of the most studied problems seems to be that of evolution and creation (see, e.g., McMullin 1985; Andersen and Peacocke 1987; Schmitz-Moormann 1992), as well as that of divine action (see Russell et al. 1998). However, there are almost no studies on the methodological issues of Darwin’s theory in relation to Catholic theology. Although Artigas et al. (2006) cite some 19th-century Catholic theologians who expressed methodological criticisms of evolutionary theory, the study is more historical than methodological.

And, most importantly, there has been no attempt, at least to my knowledge, to methodologically compare these two specific cases of the encounter between modern science and Catholic theology and to draw more general conclusions. The aim of this article is, therefore, to fill, at least in part, these three lacunae: in the methodological analysis of Darwin’s theory in relation to Catholic theology; in the methodological comparison of the two cases, Darwin and Galileo; and in offering general methodological and meta-methodological conclusions in terms of the tension between continuity and change in the methodology assumed by Church authors.

Typical problems in the relationship between science and faith concern the situation where science and religion are seen as a set of ideas or beliefs about the world and man, with science using reason and experience and theology using faith to create these ideas or theories. From this point of view, the question is: What is the relationship between these two perspectives on understanding the world and man? For example: what is the relationship between the biblical account of the creation of the world and the theory of evolution; what is the relationship between the biblical image of the world and the theories of Copernicus, Galileo, Newton, Einstein, etc.? This approach to the science–religion question can be called the “objective” approach because it involves different explanations of the world in which we live and of which we are a part.

But to answer these “objective” problems, both religion and science must give a prior answer, at least implicitly, to a question belonging to what we might call the “meta-objective” or epistemological approach: What is the cognitive status of these two different perspectives on knowing the world, scientific and religious, and how do they relate to each other in this respect? Traditionally, answers to these questions have taken the form of specific practical stances. It was not until the 20th century that theorists of the science–religion relationship began to classify these stances in terms of different positions. In this context, several possibilities have been discussed, for example, conflict, independence or separation, the supremacy of one approach over the other, integration, dialogue, etc. (cf. Stenmark 2013).

Christian theology must answer, for example, the question of whether a scientific approach opposed to a biblical or theological one can lead to a reinterpretation of Scripture and a reinterpretation of theological statements. In the case of a positive answer, it has to answer another question: Under what methodological and epistemological conditions can this happen? A negative answer to the first question must lead either to a radical separation of religious knowledge from scientific knowledge or to its superiority and supremacy over science. A positive answer, on the other hand, excludes these two extreme positions and opens the way to other intermediate solutions.

The present text does not deal with “objective” problems but with “meta-objective” issues. Assuming a positive answer to the first question in Catholic theology, I will set out to analyze the theologians’ answer to the second question, i.e., the question of the methodological and epistemological conditions that scientific theory must satisfy in order to be able to imply changes in the interpretation of Scripture and theology.

More specifically, this analysis aims to answer three questions. The first question concerns the methodological and epistemological criterion used by official representatives of Catholic theology since Galileo in their argumentation for the acceptance or non-acceptance of scientific theories as capable of influencing theology or, in other words, the criteria for a scientific theory to be a potential locus theologicus.

To answer this question, in the next three sections, I will examine three historical cases and three texts. One will concern Galileo and his conflict with the Holy Office or Roman Inquisition in the person of Cardinal Robert Bellarmine (for the use and meaning of the term “the Holy Office”, see (Fantoli [1994] 1996, pp. 35, 46) (note 63), and (Artigas et al. 2006, pp. 8f.)). The other two will concern Darwin, the first being Pius XII’s encyclical Humani Generis (AAS, vol. 37 (Pope Pius XII 1950)) and the second being John Paul II’s Address to the Pontifical Academy of Sciences (AAS, vol. 89 (John Paul II [1996] 1997)) on the theory of evolution. After a presentation of the historical background of each case, I will undertake the methodological analysis that will be guided by the two fundamental and, in fact, opposing methodological concepts of demonstration or proof (demonstratio) and hypothesis. This analysis will depend on the historical context and will, therefore, have to address other historically relevant methodological problems. Then, in the final Section 5.1, I will compare the three cases with each other, showing the similarities and differences in the methodological and epistemological criteria adopted.

On the basis of this historical and comparative analysis, another question will be posed in the following Section 5.2. It will concern the possibility of interpreting these three cases in terms of continuity and change in the methodological position of the Church’s theology over the centuries.

The answer to the second question will, in turn, be a determinant for the answer to the last question (Section 5.3): Is Catholic theology autonomous in adopting a particular methodological and epistemological stance when defining the boundary conditions for the influence of scientific theories on theology? The question is that of the dependence of theology on science itself and its historically variable nature as interpreted in philosophy, or, in other words, whether Catholic theology chooses its epistemology and methodology independently or is objectively limited in its choices by the evolution of science and its methodology. If the latter is the case, the methodology can be recognized as another specific locus theologicus, a meta-objective locus.

But before turning to the first case, that of the acceptability of Copernican theory, it is necessary to make a few preliminary remarks about the object of the study and the approach chosen.

This paper does not apply to all religions, not even to Christianity as a whole. I limit my analysis to the Catholic Church and, in particular, to its official representatives and their statements, which could be called (for a lack of a better expression) an “official” Catholic theology (“Magisterium” might be too strict, it seems). It is not limited to the teaching of Popes but also includes the statements of the Cardinals of the Holy Office (see above) and theologians who worked for this Congregation, known as Consultors, while excluding the ideas of other Catholic theologians who have not always been in full agreement with the actual statements of the Church (cf. Schmitz-Moormann 1987). This is also how I have chosen the cases studied, guided above all by their historical significance from the point of view of the science–religion relation.

However, insofar as my paper aims to make a general conclusion that goes beyond the cases studied, my text also refers more broadly to the heritage of Western Christianity before the division of the 16th century. The relationship between Catholic theology and science in Galileo’s time, and, also, in the 20th century, remains, it seems, difficult to understand without reference to the ancient theology in which it has its roots, in particular the work of Augustine of Hippo (cf. Pope Leo XIII 1893, ASS 26, pp. 282, 286; McMullin 2013).

A few remarks are also necessary regarding the research method used in this paper. The choice of three historical cases was not accidental but, as already mentioned, motivated by their exceptional importance for understanding the official position of the Catholic Church on science–religion issues. The cases of Galileo and Darwin are two of the best-known and most recognizable problems the Church has had to face that gave rise to the greatest controversy.

There is, however, a specific reason for choosing these three cases. It is the occurrence of almost identical methodological terminology in all three texts. The terms in question are “hypothesis” and “demonstration”, the former appearing in all three texts and the latter in the first two and in one of the official translations of the third text. Each time, these terms are used in opposition to one another to assess the value of the scientific theory and its capacity to influence theology. I found this terminological similarity sufficiently revealing and intellectually intriguing to ask and answer the above questions.

Moreover, these three cases will enable us to study the continuity and possible evolution of the Church’s position because they are separated in time. As is well known, the element of tradition plays an important role in the Catholic Church. But perhaps behind the declarations of continuity, we will be able also to identify significant changes.

A brief justification is also needed for the initial assumption, namely, that Catholic theology recognizes in principle the possibility of the influence of non-theological science on theology itself and the interpretation of Scripture. Of course, it is easy to identify specific situations in the history of the Catholic science–theology relationship that could be interpreted in terms of domination or separation, but I am not so much interested in individual historical cases as in certain dominant theological-philosophical trends that take the form of certain principles or rules. It seems that all three texts we are about to examine can find their common ground in certain principles formulated by Saint Augustine and in his positive solution to the question of the relationship between the interpretation of Scripture and the teachings of pagan philosophy. This position will be substantiated in the final section of this paper.

Last but not least, the drawing of general conclusions based on the analysis of three selected cases could suggest that the paper uses an inductive method of generalization. On the contrary, in line with the criticism of such an attitude in modern and contemporary philosophy of science, these three cases provide the basis for the formulation of an explanatory hypothesis, which they confirm. According to this hypothesis, generally formulated, Catholic theology can be said to have a non-absolute autonomy or a relative dependence on available methodological solutions that change over time, and for this reason, methodology can be said to be a locus theologicus in itself. The real confirmation or falsification, however, would involve testing it on other historical cases, but this is a task for another text.

2. Bellarmine’s Letter to Foscarini

2.1. Historical Background

Let us start with the analysis of the statement made by Cardinal Bellarmine in his 1615 letter to Foscarini.1

The importance of this text is exceptional as it concerns the first serious confrontation between Roman Catholic theology and the newly emerging empirical science. The cases of Galileo and Copernicus defined the modus operandi of the Roman Catholic Church for several centuries with regard to the achievements of the new science when they were in apparent contradiction with Scripture and official theology. Although the letter to Foscarini is not an official letter but a private one, Cardinal Bellarmine’s theological “prestige” was so high, as noted by Fantoli ([1994] 1996, p. 185), that even his private opinion can be considered representative of the Roman Church of that time and its posture toward Copernicus’ theory.

The letter was written in the wider context of the theological discussion triggered by Galileo’s positions on Copernicus’ theory. From the moment he made telescopic observations of the Moon, Venus, Mercury, and Jupiter in 1609–1610 (see Fantoli [1994] 1996, pp. 110ff.; cf. Finocchiaro 1985, p. 338), Galileo began to proclaim more and more boldly to the public that the fundamental assumptions of Copernicus’ theory about the mobility of the Earth and the immobility of the Sun and its central position in the Universe should be treated as true assumptions about the actual structure of the world and not simply as a purely mathematical device aimed at improving on Ptolemy’s calculations.

Galileo’s theses provoked strong reactions from many theologians. They claimed that Copernicus’ theory contradicted common sense and the common interpretation of Scripture. Galileo accepted the challenge. He began to defend his position for several years. This defense took the form of a theological dispute over the principles of scriptural interpretation. Galileo wrote several detailed letters on the subject, which he circulated among leading figures in ecclesiastical and theological circles in Rome. He also submitted some of these polemical letters to Cardinal Bellarmine, a member of the Holy Office, for his opinion.

However, some theologians supported Galileo in his defense of Copernicanism. Among them was Foscarini, superior of the Carmelite order in Rome. At the beginning of 1615, he published a short letter in which he defended the thesis that Copernicus’ theory could be reconciled with the affirmations of Scripture. This work having been severely criticized by a consultor of the Holy Office, Foscarini wrote up the defense and sent it, along with the original text, to Bellarmine for his opinion. Bellarmine’s opinion was formed very quickly, and Foscarini received the letter as early as April of the same year (see McMullin 2013, p. 208n.; Arcangeli 2016). In it, Bellarmine presents his personal and, at the same time, quasi-official position on Copernicus’ theory.

Let us quote the two most epistemologically and methodologically important passages from Bellarmine’s letter:2

First I say that it seems to me that your Paternity and Mr. Galileo are proceeding prudently by limiting yourselves to speaking suppositionally3 and not absolutely, as I have always believed that Copernicus spoke. For there is no danger in saying that, by assuming4 the Earth moves and the sun stands still, one saves all of the appearances better than by postulating eccentrics and epicycles; and that is sufficient for the mathematician. However, it is different to want to affirm that in reality the sun is at the center of the world and only turns on itself, without moving from east to west, and the earth is in the third heaven and revolves with great speed around the sun; this is a very dangerous thing, likely not only to irritate all scholastic philosophers and theologians, but also to harm the Holy Faith by rendering Holy Scripture false …

Third, I say that if there were a true demonstration5 that the sun is at the center of the world and the earth in the third heaven, and that the sun does not circle the earth but the earth circles the sun, then one would have to proceed with great care in explaining the Scriptures that appear contrary; and say rather that we do not understand them than that what is demonstrated is false. But I will not believe that there is such a demonstration, until it is shown me. Nor is it the same to demonstrate that by supposing the sun to be at the center and the earth in heaven one can save the appearances, and to demonstrate that in truth the sun is at the center and the earth in the heaven; for I believe the first demonstration may be available, but I have very great doubts about the second, and in case of doubt one must not abandon the Holy Scripture as interpreted by the Holy Fathers.

(Bellarmine 1989, pp. 67f., italics are mine)

Several expressions by Bellarmine in which he sets out his views on the two fundamental assumptions (suppositions) of Copernicus’ theory—the thesis of the Earth’s mobility and the thesis of the Sun’s immobility—deserve particular attention and epistemological or methodological analysis.

These are essentially expressions derived from Aristotle’s logic, which was the basis of scholastic philosophy and theology, to which Bellarmine refers in his letter. This logic was, in fact, at the heart of the entire scientific culture of the time; Galileo himself claimed that he was always guided by Aristotle’s logic in his research and that he shaped his scientific method on this very basis (see Galileo 1896, vol. 18, p. 248; cf. Wallace 1988a, p. XIII). Of course, there were many different interpretations of this logic, but the basic categories were the same.

It is worth noting that Galileo and Bellarmine were essentially inspired by the same Aristotelian logical tradition developed at the Jesuit Collegio Romano. Bellarmine studied logic in the 1560s with the Jesuit Francesco Tomitano. Galileo studied Aristotle’s logic privately in the late 1580s, most probably on the basis of manuscripts by Tomitano’s disciples and successors at the Collegio Romano—Lorini and Vallius (see Wallace 1988a, pp. XVIIIff.).

However, at the time of the theological discussion in question, Bellarmine’s and Galileo’s views on Aristotle’s logic, in particular on the ideas of demonstration and hypothesis, diverged significantly. This fact was probably one of the most important reasons for Galileo’s condemnation in 1616 as it made mutual understanding between Galileo and the Holy Office almost impossible. Although they used the same logical terms, they gave them different meanings.

2.2. The Demonstration and Hypothesis by the Time of Galileo

The Aristotelian understanding of science was based on the idea of demonstrated knowledge. However, not all kinds of demonstrations were expected to meet the criteria of scientificity or true demonstration. In this line, Bellarmine makes a distinction between a true demonstration and a demonstration ex suppositione or ex hypothesi.6 By drawing this distinction, Bellarmine claims that the latter is not a true demonstration and, as a result, is not concerned with reality but only with mathematical calculations. With this, he expresses another Aristotelian axiom, namely, that only physics and metaphysics are genuine sciences that present the true causes of things. Mathematics, on the other hand, because of its idealization cannot be about the real world or physical causes. A true demonstration should be physical or metaphysical rather than mathematical.

However, two opposing interpretations of this passage of Bellarmine’s statement have emerged in historiography (see Giostra 2015, p. 258). One, which can be described as the received view, defends—in line with the position taken by Andreas Osiander in his anonymous “Notice to the Reader” to the first edition of Copernicus’ De Revolutionibus—the so-called mathematical “fictionalism” of Bellarmine and the Jesuits of the Collegio Romano (cf. Ashworth 1986, p. 158; Fantoli [1994] 1996, p. 23). According to the fictionalist view, Bellarmine saw mathematical astronomy (both Ptolemaic and Copernican) as mere fictional tools for describing celestial movements and “saving phenomena”, without any implications regarding the real or physical structure of the world.7 In the 1980s, Ugo Baldini challenged this view. According to him, the Jesuits of the Collegio Romano and Bellarmine himself did not exclude the possibility of relating mathematical astronomy to the real world on the condition of providing physical proof (i.e., based on Aristotle’s physics) of their assumptions (see Baldini 1992, pp. 292f. 316f.; cf. Giostra 2015, p. 259; Coyne and Baldini 1985, pp. 105f.). Baldini’s interpretation of Bellarmine’s words was, however, alien to Galileo himself. Galileo’s reply (cf. note 11 below) shows that he interpreted these words as an expression of the “fictionalist” approach.

The term “true demonstration” does not appear in the logical writings of Aristotle. However, in the Posterior Analytics (I, 3), a work that presents his logical theory of scientific knowledge, he contrasts a demonstration in the strict sense, in Latin translations demonstratio simpliciter (i.e., demonstration without qualification), with a demonstration in the broad sense, i.e., with qualifications—demonstratio secundum quid in Latin—which arises when some of the necessary conditions of the demonstration in the strict sense are not fulfilled (cf. Zabarella 1586, pp. 411f., 423f.; cf. Baldini 1992, pp. 308ff.). A demonstration from supposition (ex suppositione or ex hypothesi) is a demonstration in the broad sense because its premises are not absolutely true as is required for a true demonstration or demonstratio simpliciter but only accepted as true conventionally by agreement.8 The renowned Paduan logician and natural philosopher Giacomo Zabarella (see Liana 2020, pp. 59ff.; Mikkeli and Baker 2024), who exerted considerable influence on the Jesuits from the Collegio Romano and, consequently, on Galileo (see Wallace 1988a, 1988b, 1995; de Jong 1989), in his commentary on the distinction made by Aristotle, stated that knowledge acquired from a supposition is, in fact, not knowledge at all.9

We can, therefore, reasonably assume that it was this Aristotelian epistemological distinction that led Bellarmine to claim in his letter that it would be one thing to demonstrate that the earth actually moves and that the sun remains motionless at the center of the world and quite another to demonstrate celestial phenomena simply by hypothetically assuming the truth of these (“by supposing”). McMullin’s (1998, p. 279) claim that Bellarmine’s fictionalism had biblical rather than Aristotelian origins does not contradict this hypothesis. If McMullin is correct, only Bellarmine’s motivation would be different, but the idea of fictionalism itself remains Aristotelian. The same is true of Baldini’s interpretation.10

Thus, according to Bellarmine, the two basic hypotheses of the Copernican theory are not true, either in themselves or demonstrated by a true demonstration, but only hypothetically. As such, they cannot influence the interpretation of the Holy Scripture. Only if they were demonstrated as truths, should theologians begin to think about changing the literal interpretation of the Bible.

As mentioned above, Galileo, defending himself against Bellarmine’s theses, wrote several short papers.11 His defense went in several directions. From our point of view, two arguments are the most important. Firstly, Galileo refutes Bellarmine’s narrow interpretation of the Aristotelian idea of “supposition”. In his view, we need to distinguish between two types of suppositions in astronomy (Galileo 1895, pp. 357ff.; cf. Moss 1985, p. 45). Alongside the frivolous ideas of human imagination, there are also true hypotheses (ipotesi vere, supposizioni vere), demonstrated by necessary demonstrations (dimostrazioni necessarie). In the case of such hypotheses, the demand is for recognition of their absolute truth in relation to the nature of the world.12 Secondly, he considers his own necessary demonstrations of Copernicus’ suppositions as true demonstrations, sufficient to recognize the necessary truth of these suppositions and to reject the contrary theses adopted by Ptolemy and his followers. Consequently, he regards the Copernican suppositions as sufficiently demonstrated to require a reinterpretation of the Scripture on these matters.

Both of Galileo’s arguments were well supported by the Aristotelian logical tradition. In his Posterior Analytics, Aristotle gives the term “hypothesis” or “supposition” several meanings, the primary of which designates true and demonstrated principles of a demonstration simpliciter, as opposed to axioms and definitions that are known in themselves (cf. Posterior Analytics, I, 2; in Bekker’s numbering 72a, 15–24). From this point of view, there can be a true demonstration from a supposition, which is the opposite of the demonstration ex suppositione mentioned by Bellarmine, i.e., a demonstration from a mere supposition or hypothesis.13 The discussion of the Aristotelian understanding of supposition in the context of true demonstration can be found in all Renaissance commentaries on the Posterior Analytics.

The idea of a true demonstration, different from the perfect demonstration simpliciter, was also developed in Aristotelian schools of logic, particularly in the Italian Padua. It took the form of the so-called regressus. In his Posterior Analytics (I, 13), Aristotle gave yet another typology of demonstration, more relevant to the theory of scientific knowledge. He distinguished between a demonstration from a cause and a demonstration from an effect. The former is identical to the perfect demonstration simpliciter, while the latter is a less perfect demonstration with qualification (secundum quid), in which one of the conditions necessary for the perfect demonstration, namely, knowledge by means of a cause, is not fulfilled (see Zabarella 1586, pp. 418, 420ff.). The criterion for this division was ontological since scientific knowledge (episteme), as Aristotle understood it, had to be knowledge of the belonging of a certain attribute to a certain thing by means of a necessary and immediate cause. Thus, the perfect demonstration simpliciter was to provide such causal knowledge.

Aristotle called the causal demonstration dioti and the demonstration from effect hoti. In the English literature, they are sometimes referred to as “why-demonstrations” and “fact-demonstration”, respectively (cf. Berquist 2007). The Latin tradition developed specific names. A why-demonstration was commonly called “demonstratio propter quid”. Sometimes, it was also referred to as “demonstratio a priori” where “a priori” means that the premises must be prior to the conclusion, not from the point of view of the knower (or, as Aristotle says, better known to us) but rather in the order of nature (in themselves). In this latter sense, the cause is “naturally” prior to the effect. Such demonstrations were supposed to give knowledge of the effect by means of its necessary cause found in the middle term of the demonstrative syllogism.

The fact-demonstration, on the other hand, has been given many different names in the Latin tradition: demonstratio quod or demonstratio quia or a posteriori. The demonstration that proceeds from effect to cause is just one type of fact-demonstration14. According to Aristotle, such a demonstration led to knowledge of an unknown (to us) cause from a known (to us) effect. It was about a fact because it demonstrated only the existence of a cause from the knowledge of the existence of an effect. It, therefore, provided only factual knowledge of the cause, without any knowledge of its nature and essence. On the contrary, in the perfect demonstration simpliciter, such a cause had to be known at the outset not only as existing but also as the cause of the effect: either as a self-evident primary cause or as a secondary cause demonstrated by means of a demonstration simpliciter.

It was, therefore, commonly accepted among Aristotelians that, on purely logical grounds, only demonstratio simpliciter was able to provide true knowledge of things. However, during the Renaissance, natural philosophers and logicians came to realize that perfect demonstratio propter quid was suitable mainly for metaphysics and mathematics but not for the natural sciences (esp. physics and medicine), and that this type of demonstration is practically non-existent in these sciences. Natural causes are largely unknown to us, to use Aristotle’s terms, so they have to be first discovered and demonstrated to exist from known effects and not simpliciter (cf. Zabarella 1586, pp. 418, 424ff.).

The Idea of Regressus

A problem had to be solved. If the natural sciences do not use perfect why-demonstrations, they cannot be sciences at all, or, at least, they must be reduced to a very restricted domain. This conclusion, however, ran counter to the common belief that the natural sciences were true sciences. The problem, then, was how to preserve the scientific status of the natural sciences and how to work out an appropriate why-demonstration for them.

To solve this problem in line with Aristotle’s teaching, logicians at the school of Padua, where the empirical medical tradition had developed since the Middle Ages, developed the idea of the regressus procedure. The problem of regressus became one of the most fundamental and debated logical problems in the Renaissance. Contemporary research on Galileo shows that he took the idea of the regressus from the logicians of the Collegio Romano, who, in turn, had taken it from Paduan Giacomo Zabarella. Moreover, Galileo developed it in a highly creative way.15

In the most general terms, the regressus procedure was aimed at transforming an imperfect fact-demonstration into a perfect why-demonstration. From a formal point of view, it was a simple procedure consisting of the appropriate rearrangement of the three terms of the syllogism.16 But from an epistemological point of view, it was necessary to introduce an additional intermediate step in order to render a distinct (cognitio distincta) cause by which the initial effect was to be demonstrated and which was only known in a confused way (cognitio confusa) through the initial fact-demonstration. In the Paduan tradition, this step took the form of a specific intellectual analysis, called mental exchange (negotiatio) or mental examination (examen mentale), or mental consideration (mentalis consideratio). Galileo speaks only of an “intermediate stage”. According to Wallace (1995, p. 95), it was this intermediate stage of the regressus that Galileo developed most ingeniously, using, for example, mathematical demonstrations.

As we can see, the demonstrations built on the basis of regressus, and such were those Galileo put forward in support of his assumptions challenged by Bellarmine, were not, because they could not be, true demonstrations in Bellarmine’s sense, i.e., demonstrations simpliciter based on premises known by themselves.17

We will not go any further into this dispute. Let us confine ourselves to drawing a few conclusions relevant to the rest of the analysis. The dispute was essentially logical and methodological and concerned the understanding of “true” demonstration and the notion of demonstration ex suppositione.18 Bellarmine, at least in Galileo’s eyes, took from Aristotelianism a very narrow understanding of hypothesis as an entirely arbitrary supposition, for which there is no place in a true demonstration, which must proceed from premises that are first true by virtue of a kind of intellectual self-evidence. According to this point of view, which we will call conservative, Copernicus’ theory could not acquire scientific status because of the impossibility of providing demonstrations simpliciter of its two basic premises. Galileo, as a naturalist, better understood the limited nature of demonstrations simpliciter and used the idea of regressus, foreign to Bellarmine and the Holy Office, according to which demonstrations ex suppositione can also be true demonstrations and hypotheses can become well-proven theses, but not simpliciter or the way expected by Bellarmine.

In Baldini’s different approach to Bellarmine’s letter, this conclusion would have to be somewhat different without recourse to the idea of demonstration simpliciter. But as we have said, Galileo understood this letter in a very traditional way; and it is likely that many theologians of the Holy Office would have done the same. Baldini (1992, p. 292) acknowledges that famous Jesuit philosophers of the time, who did not belong to the Collegio Romano, presented the traditional, conservative Aristotelian approach to the methods of astronomy and physics and to the idea of demonstratio simpliciter. Therefore, more conservative theologians were more likely to adopt this position.

3. Humani Generis of Pius XII

3.1. Historical Background

The second text is Pius XII’s encyclical Humani Generis (AAS 37 (Pope Pius XII 1950))19, in which he addresses the theory of evolution and its relationship with theology.20

Its importance lies in the fact that it is the Roman Church’s first official statement on the theory of evolution. This is not to say that Catholic theologians and Vatican officials had not noticed the theory’s emergence beforehand. Only a dozen years after the publication of Darwin’s On the Origin of Species, the first articles by Catholic theologians supporting the theory of evolution and proclaiming its compatibility with Scripture and the Christian faith were published. From the outset, these articles were accompanied by denunciations to the Holy Office by theologians who considered the theory of evolution to be contrary to Church teaching.21 At the time, however, the Holy Office wanted to avoid openly condemning the theory of evolution. Perhaps it was preoccupied with the still vivid memory of the Galileo affair and the Church’s discreet withdrawal from the condemnation of Copernicus’ theory at the beginning of the 19th century (cf. Fantoli [1994] 1996, pp. 496ff.). Awareness of the similarity between the two cases is strikingly attested to by the first decree of the Congregation of the Index in 1878 on the placing on the Index of Caverni’s book, quoted in the English translation by Artigas et al. (2006, p. 47):

De’ nuovi studi della filosofia. Discorsi di Raffaello Caverni a un giovane studente. This work merits serious and special attention. In it, Darwinism is expounded and partly approved … Until now the Holy See has rendered no decision on the system mentioned. Therefore, if Caverni’s work is condemned, as it should be, Darwinism could be indirectly condemned. Surely there would be cries against this decision; the example of Galileo would be held up; it will be said that this Holy Congregation is not competent to emit judgements on physiological and ontological doctrines or theories of change. But we should not focus on this probable clamor. With his system, Darwin destroys the bases of revelation and openly teaches pantheism and an abject materialism. Thus, an indirect condemnation of Darwin is not only useful but even necessary, together with that of Caverni, his defender and propagator among Italian youth (italics are mine).

The decree was adopted unanimously by nine cardinals. Pope Leo XIII approved the decree, giving it the force of law (ibid., pp. 47f.), but the content of the decree was never published, and only its existence and the legal effect of the ban on the distribution of Caverni’s book became known, without the reasons for the ban being made public. It was, therefore, not explicitly known that the condemnation concerned Darwin’s theory of evolution (ibid., pp. 13ff., 47).

In later cases, persuasion and “behind-the-scenes” pressure were also used on individual Catholic authors who supported the theory of evolution to withdraw their books from print themselves or to retract them publicly. In return, they were promised that no official action would be taken against them. Nevertheless, these cases were relatively well known to the Church and theologians, if only through the Catholic press.22 All this created a widespread opinion that the Church tacitly rejects de facto the theory of evolution (see ibid., pp. 270–83). Today, we also know that the work of the famous Jesuit and paleontologist Pierre Theilard de Chardin in the first half of the 20th century in favor of reconciling the Christian faith with the idea of biological evolution was one of Pius XII’s motivations for speaking out on the theory of evolution.23

As can be seen, prior to the publication of Pius XII’s encyclical, the Vatican’s position on the theory of evolution remained deeply hidden in the Vatican archives, and its disclosure to the public took the form, at most, of leaks in the Catholic press and much speculation about a few decisions of the Congregation of the Index. The encyclical was, therefore, the first official voice of the Roman Church on the subject.

However, the encyclical Humani Generis was not intended by its authors to focus on the theory of evolution. Its main aim was to defend traditional scholastic24 and neo-Thomistic theology and philosophy against the growing onslaught of new philosophical currents, such as existentialism, materialism, or historicism, to which more and more Catholic theologians and philosophers were adhering (see Dondeyne 1951, pp. 14–16). But for the encyclical’s authors, one of the most pernicious new ideas was the philosophical idea of a universal or cosmic evolution designed to explain “the origin of all things”. According to the encyclical, proponents of this idea preached “the monistic and pantheistic opinion that the world is in continual evolution” (HG 5), and that there is, therefore, no Absolute and no unchanging essence of things.25 By contrast, for scholastic and neo-scholastic philosophy and theology, the idea of an Absolute and the idea of an unchanging essence of things were beyond question.

The essential subject of the encyclical was therefore strictly philosophical questions in their relation to Catholic theology. The problem of the empirical theory of evolution appears, as it were, on the margins of the fundamental philosophical problem. Questions relating to the theory of evolution occupy less than 10% of the text of the encyclical (HG 5 and HG 35–37).

3.2. Methodological Statements on Evolution

In its first section (HG 5), the encyclical states that the theory of evolution is the specific source of this mistaken philosophical idea of universal evolution. At the same time, the encyclical asserts that philosophers have accepted this theory too hastily, given that it has not yet been “fully proved” (Latin: invicte probata)26 in the empirical sciences. So here, we have the same methodological thesis as in Bellarmine’s letter, namely, that a scientific idea must first be fully proven before it can be an authentic source of philosophical, let alone theological, ideas.

The encyclical deals at greater length with the Darwinian theory of evolution in its final section (HG 35–37). In giving the reason for this interest, the Pope emphasizes that it directly affects the Church’s teaching on the creation of man and the interpretation of the text of Genesis in Scripture. In this context, the encyclical addresses three questions: the evolutionary origin of the human body, the evolutionary origin of the human soul, and the question of polygenism.

The encyclical excludes from the outset the possibility of freely discussing the question of the evolution of the human soul. The basic argument is derived from a dogma of faith: “for the Catholic faith obliges us to hold that souls are immediately created by God” (HG 36).

The encyclical also prohibits Catholic theologians from freely discussing polygenism on the question of the origin of the human body because, as it states, “now it is in no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin” (HG 37). This prohibition, as can be seen, is considerably weaker than the previous one, and the statement itself is sufficiently ambiguous to have provoked much speculation about Pius XII’s real intentions regarding polygenism. Roman cardinals tried to clarify the formula but to no avail. Pius XII explicitly told the cardinals that the encyclical’s formulations were “deliberately cautious and that it is good that it should remain as it is, without further clarification” (see Kemp 2023, p. 25).

The situation is quite different, however, when it comes to the evolution of the human body. Given “the present state of the human sciences and sacred theology”, the encyclical states that the Church “does not forbid”27 (HG 36) the study and discussion of this question by “men experienced in both fields”, subject, of course, to certain conditions defined by the Church’s Magisterium.

These three methodologically different positions of the Church find their justification in the encyclical in the form of conditions that must be met by scientific theories in order for them to cause any change in Catholic theology. The encyclical also tells how to proceed when these conditions are not met.

From a methodological point of view, the encyclical contrasts demonstrated knowledge with hypotheses having only “some sort of scientific foundation” (HG 35). The encyclical also calls the latter “conjectural opinions” (Latin: opiniones coniecturales, HG 35. 37). According to the encyclical, “conjectural opinions” must be rejected if they directly or indirectly contradict the dogmas of the Church. This is undoubtedly the situation in the case of the question of the creation of the human soul. In the case of polygenism, the situation is more complicated since the encyclical merely states that, given the current state of science and theology, it is impossible to see how this hypothesis can be reconciled with the dogma of original sin. It thus suggests that the situation could change in the future.

However, with regard to the human body, it is possible to theologically examine the evolutionary hypothesis, that is, the hypothesis of “the origin of the human body as coming from pre-existent and living matter”. The discussion, nevertheless, cannot be completely free. The status of an unproven hypothesis implies that the theory of evolution should be considered by theologians and scientists on an equal footing with the opposite hypothesis (HG 36):

However, this must be done in such a way that the reasons for both opinions, that is, those favorable and those unfavorable to evolution, be weighed and judged with the necessary seriousness, moderation and measure.

Moreover, both sides in this discussion should be willing to submit to the final judgment and decision of the Church, which alone has the authority to interpret Scripture and the dogmas of the faith authentically.

Here we are dealing with a kind of usurpation on the part of the Church’s Magisterium to determine the cognitive value of all those scientific hypotheses that have not been demonstrated, and which contradict the very foundations of the Christian faith. This interpretation is confirmed by a text by Karl Rahner, one of the most prominent theologians of the time. In a text on the question of monogenism and polygenism, he writes that the terms “coniecturalis opinio” and “hypothesis”, which the encyclical applies to the question of polygenism (but also to the theory of evolution), mean that these concepts can be considered false (empirically) and rejected on the basis of a source of knowledge other than natural science, thus suggesting theological sources (see Rahner 1963, p. 232).

It should be noted, however, that Rahner’s interpretation was not a common one, especially among followers of neo-scholastic philosophy. A different and more conciliatory interpretation of the encyclical was given, for example, by Dondeyne (1951, pp. 14–16). He agrees with the charges against the encyclical that the Pope’s expressions unnecessarily diminish the “soundness” and “degree of certainty of the evolutionist hypothesis”. But he does not think they should be taken too seriously (“il n’y a pas de quoi s’émouvoir outre mesure”; ibid., p. 16). These should not be taken too literally as the Pope does not make infallible statements about the status of empirical sciences. The encyclical is not even a philosophical document, let alone a document on empirical sciences. At best, the Pope’s wording should be considered an embarrassing way of expressing his caution by a theologian who does not quite need to know about the sciences and is looking at them from the point of view of someone forced to look at them from the outside.

Thus, it can be said that the methodological position of Humani Generis represents a kind of radicalization of Bellarmine’s position in his letter to Foscarini. Like Bellarmine, Pius XII believes that a scientific theory should be proven beyond all doubt in order to imply modifications of theological ideas. Unproven hypotheses cannot be taken seriously by theologians. A peculiar novelty in relation to Bellarmine is revealed in the thesis that the Church can have the final say on the veracity of such conjectural natural hypotheses insofar as they do not agree with the traditional interpretation of Scripture and faith. Bellarmine’s position is implicit, whereas Pius XII formulates it explicitly. Humani Generis continues in this regard the line taken by the Magisterium of the Roman Church from the 2nd half of the 19th and early 20th centuries.28

And yet, despite the similarities, the methodological positions of Bellarmine and Pius differ significantly. This difference is rooted in different historical and philosophical contexts, more specifically, in a different methodology of empirical science. While both are based on scholastic methodology, with its roots in the logic of Aristotle, Pius XII’s text shows the influence of a different methodology, in particular the 19th-century version of modern empiricism. The encyclical does not explicitly adopt the methodological formulations of modern empiricism; nevertheless, many of the expressions used in the encyclical do not seem to be reconcilable with the traditional scholastic view of Aristotle’s conception, to which Bellarmine and the Holy Office referred in the Galileo case.

3.3. “Humani Generis” and Empiricist Tradition

Let us pay attention to the three formulations of the encyclical. Since the English translation is not a faithful translation of the text of the Latin original, but a peculiar interpretation of it, I give these texts in both English and the original Latin:

(1)

“in the case of clearly proved facts” (HG 35); Latin: “ubi de factis agitur reapse demonstratis”,

(2)

“when there is rather a question of hypotheses, having some sort of scientific foundation” (HG 35); Latin: “ubi potius de ‘hypothesibus’ sit quaestio, etsi aliquo modo humana scientia innixis”,

(3)

“they act as if the origin of the human body from pre-existing and living matter were already completely certain and proved by the facts which have been discovered up to now and by reasoning on those facts” (HG 36); Latin: “ita sese gerant quasi si ipsa humani corporis origo ex iam exsistente ac vivente materia per indicia hucusque reperta ac per ratiocinia ex iisdem indiciis29 deducta, iam certa omnino sit ac demonstrata”.

First of all, the term “fact” (Latin: factum) used in the encyclical in the context of the scientific method is foreign to traditional Aristotelian terminology. In that tradition, as in other pre-modern traditions, the Latin term “factum” occurred at most as the name of a human work or other causal agent, in its basic participle sense of something done or made. The reference to natural phenomena did not appear until the empiricism of Francis Bacon, and then in the 17th-century empiricism of the English Royal Society (cf. Shapiro 2000, pp. 105ff.). The ideas of English empiricism were developed in the 19th century when the concept of fact became common in the methodology of empirical sciences.

Moreover, the phrase “proved facts” (de factis demonstratis) occurring in the encyclical refers to the specific notion of general fact corresponding to the notion of law in 19th-century empiricism (cf. e.g., Herschel 1831, pp. 102, 175, 185; Comte 1830, p. 5). To speak of the demonstration of a particular fact would bear the hallmarks of a typical overstatement, especially since the Latin text speaks of the demonstration of these facts on the basis of reality itself (reapse), that is, on the basis of experience or particular facts. Moreover, the word “reapse” comes from the language of Aristotelianism and scholasticism, which the English “clearly” does not fully capture.

A further remark also applies to the English translation. In the Latin original, the word “factum” occurs only once, while in the English translation the word “fact” appears three times. The last two occurrences render the Latin “indicium”. It is an ambiguous word and can be translated as “indication”, “sign”, “evidence”, or “fact”. It can be relatively easily related to the methodological terminology of Scholasticism and Aristotelianism where demonstration from effect was also called “demonstration from the sign” (a signo) (cf. Zabarella 1586, pp. 261, 426). In this Aristotelian perspective, “indicium” would mean the observable effect of a hidden cause. This type of a posteriori method always starts from particular sentences, that is, from particular facts. The English translation, thus, refers to the terminology of empiricism to an even greater extent than the Latin original.30

Another expression that draws on the empiricist tradition is “hypotheses, having some sort of scientific foundation” (aliquo modo humana scientia innixis). The encyclical is not concerned with the nature of this link, but such a methodological link between hypotheses—understood as unproven explanations of phenomena—and science is in itself a procedure foreign to Aristotelianism and Scholasticism.

In the methodology of the sciences, the notion of hypothesis appeared only in the 17th century in the aforementioned Royal Society, usually in connection with the notion of fact (see Shapiro 2000, pp. 143–45). Similarly, the encyclical links these two concepts. However, it was not until 19th-century empiricism that a methodological understanding of the heuristic function of hypotheses in science was developed. Guided by the already widespread awareness of the limitations of the empirical method developed by Bacon and by analyses of the changing practice of science, authors such as Auguste Comte, John F. W. Herschel, and John S. Mill introduced the concept of hypothesis into the very heart of the heuristic method in science. Mill speaks explicitly of the “Hypothetical Method” in science (Mill 1843b, p. 13).

In the view of these authors, hypotheses were an effective tool for the search for new laws and theories and, ultimately, for true causes (verae causae) in nature.31 However, this was new to the ideas of the founders of English empiricism, Bacon and Newton. Newton maintained that there was no room in science for any hypothesis, either metaphysical or physical. He is famous for the phrase “hypotheses non fingo” (I frame no hypothesis), which appears in the Scholium generale added to the second edition of the Principia (see Newton 1713, p. 484; [1848] 1995, pp. 442f.).32

Herschel writes that one should not be afraid to create hypotheses and theories. With hypotheses, new putative causes are introduced into theories, by which they “afford us motives for searching into analogies” (Herschel 1831, p. 196).

However, all empiricists, whether Herschel, Mill, or Comte, were aware of the arbitrariness of hypotheses. Their use in science, therefore, had to be subject to methodological limitations. They could not be completely arbitrary ideas but ideas built on the basis of previous experience and logically linked to the whole network or classification of previous knowledge (cf. Mill 1843b, pp. 10ff.). The most important feature of scientific hypotheses, however, was to be the possibility of transforming them into true or false sentences about reality, by verifying or refuting them on the basis of empirical predictions deduced from such hypotheses and theories.

From a logical point of view, the idea of deductive and empirical verification, then called the deductive method, was a new, inverted version of Bacon’s method of complete induction, necessary to justify the use of hypotheses and theories in science (cf. Mill 1843b, p. 13). Whereas Bacon’s inductive method was to consist in a critical analysis of experience and its progressive generalization, deductive verification was to consist in checking all the individual predictions or effects of an assumed hypothesis, i.e., the facts predicted by the hypothesis. This is why the empirical methodology of the 19th century refers to the demonstration, not just the confirmation, of hypotheses or theories by facts. Mill (1843b, p. 15) puts it as follows:

It appears, then, to be a condition of a genuinely scientific hypothesis, that it be not destined always to remain an hypothesis, but be certain to be either proved or disproved by that comparison with observed facts which is termed Verification.33

We can, therefore, assume that when the author of the encyclical criticizes the position of those who treat the hypothesis of the origin of man as if it had already been deduced on the basis of the facts gathered so far and the relevant reasoning (per indicia hucusque reperta ac per ratiocinia ex iisdem deducta), and thus, as if it were already completely certain and demonstrated (iam omnino certa sit ac demonstrata), he alludes (consciously or not) to the methodological ideas of empiricism and, in particular, to the ideas of induction and verification.34

However, another interpretation cannot be ruled out either: namely, that the author of the encyclical had in mind Aristotle’s imperfect fact-demonstration, that is, proof from effects or signs, and that he interpreted the method of modern empirical sciences this way. But then he would be accepting as authentic proof what Galileo unsuccessfully defended in his polemic with Bellarmine and the Holy Office as sufficient “dimostrazioni necessarie”.35

Regardless of the interpretation chosen, in both cases, there is a significant departure from the ideal of scientific knowledge (episteme) and the ideal of demonstratio simpliciter adopted by scholastic philosophy from Aristotle. Neither induction by generalization nor verification nor proof from effect is by any means a perfect demonstration simpliciter of Aristotle’s logic.

Therefore, it is clear that the authors and translators of the encyclical were, consciously or not, influenced by 19th-century empiricism and its ideal of scientific knowledge, different from the Aristotelian and scholastic ideal.

The concession to a new ideal of scientific knowledge on the part of official ecclesiastical neo-scholasticism was not, however, devoid of justification. Indeed, there is a link between the epistemology of modern empiricism and the epistemology of the neo-scholastic encyclical. Although modern thought from the outset rejected Aristotelian induction as a reliable method of knowing first principles and, also, to a large extent, the idea of syllogistic demonstration, it nevertheless retained elements of the Aristotelian ideal of scientific knowledge as certain, true, and, above all, demonstrated. Today, this new ideal is sometimes referred to as the Bacon—Descartes ideal (see Watkins 1984, pp. 126ff.). Admittedly, the new understanding of the ideal criteria of scientificity (certainty, truth, and demonstration) was significantly different from Aristotle’s. Moreover, it was otherwise different in rationalism and otherwise in empiricism, but the original terminology and intuitions remained the same. A plausible hypothesis can be advanced, it seems, that the use of the same terminology by neo-scholasticism and modern epistemology was that necessary common minimum, which, over time, enabled different methodological and epistemological paradigms to converge. Without such a convergence, it seems unthinkable that neo-Thomistic authors—at least some of them—would recognize the new empirical science as authentic knowledge capable of effecting a change in the interpretation of Scripture and theology, insofar as it is true and demonstrated knowledge and not merely hypothetical.36

3.4. Darwin Confronts Empiricism: A New Idea of Scientific Hypothesis

The idea of a common element also makes it possible to understand the astonishing compatibility of empiricism and neo-scholasticism in the 19th century (and the following century too) in casting doubt on the scientific character of the natural selection hypothesis. The encyclical’s contention that the theory of evolution is not sufficiently justified in “facts” or “indicia” largely reflects 19th-century empiricism’s critique of the theory of evolution.37

As soon as On the Origin of Species was published, Darwin’s good friends and acquaintances with whom he corresponded, such as Asa Gray, questioned the idea of natural selection as an adequate true cause (vera causa). Darwin himself mentions it in his letters, for example to Charles Lyell from 23 February 1860 (see F. Darwin 1887, vol. 2, pp. 289f.). And yet Newton’s idea of vera causa was fundamental to the methodology of British empiricism.

Similar criticisms of Darwin’s theory were also voiced by John Herschel, whose methodological texts Darwin appreciated and studied. In a brief note accompanying his earlier article, Herschel (1861) rejected the idea of natural selection as the governing cause of organismal evolution, accusing it of being an arbitrary, fictitious, and “mysterious” explanation of the mechanism of transformation. In his view, its explanatory value was comparable to that of explaining the origin of Shakespeare’s or Newton’s works by a purely random and mechanical juxtaposition of letters and words, in the manner typical of the fictional inhabitants of the flying island Laputa from Swift’s Gulliver’s Travels:

We can no more accept the principle of arbitrary and causal variation and natural selection as a sufficient account, per se, of the past and present organic world, than we can receive the Laputan method of composing books (pushed à l’outrance) as a sufficient one of Shakespeare and the [Newton’s] Principia.

(Herschel 1861, p. 12)

The idea of natural selection in no way satisfied the postulate of verification. As a “mysterious” force, it did not allow empirical predictions to be derived and tested. It remained a fictional idea of the imagination, the veracity of which could not be established by experience and facts. Therefore, it did not meet the criteria of scientificity adopted by 19th-century empiricism. As Charles H. Pence put it38:

It should start to be clear, then, why Herschel wouldn’t have liked Darwin’s science. There was just no way, given the biological knowledge available at the time (or even available now!) to go look at every single change in the history of life, and think about how to describe it in terms of natural selection. And there was no way in Darwin’s day to go produce new cases of natural selection to make sure that it worked right.

(Pence 2021–2022)

Darwin had his own answer to these objections. We cannot discuss Darwin’s epistemology in detail here, so we will confine ourselves to two pertinent observations.

The first concerns the question of true cause (vera causa) and the “mysterious” nature of natural selection. Darwin was well aware that he could not explain the intrinsic nature of natural selection, what it is, and its internal mechanism. However, he found an extremely strong historical argument in his favor and against his critics. Reading David Brewster’s Life of Newton (cf. Brewster 1855, pp. 282ff.), Darwin discovered that an almost identical objection regarding vera causa was also made by Leibniz against Newton and his force of gravity, namely, that he could not show what gravity itself is.39 Leibniz accused Newton that the force of gravity he had introduced was an “occult quality”, not just one whose cause is merely unknown but cognizable but one that transcends the nature of creatures and is rather proper to God himself.40 So, even if Darwinian natural selection remained a mysterious or occult force, it was undoubtedly one in good company that 19th-century empiricists did not question. So, in Darwin’s mind, the proponents of empiricism were not entirely consistent in criticizing his idea of natural selection.

Secondly, Darwin had different views from 19th-century empiricists on the status of hypotheses and theories in science and on the role of verification. In this respect, William Whewell’s ideas were closer to his own than Herschel’s (cf. Thagard 1977; Ruse 1975). In 1856, even before the publication of On the Origin of Species, he wrote of his hypothesis, called elsewhere “natural selection” (see E. Darwin 1841, C9v; Barlow 1963, p. 205), that it was neither definitive nor the best formulated, but that it would probably be replaced in time by a better hypothesis. This, he thought, was the typical way of doing science:

To be brief, I assume that species arise like our domestic varieties with much extinction; and then test this hypothesis by comparison with as many general and pretty well-established propositions as I can find made out,—in geographical distribution, geological history, affinities, &c. &c. And it seems to me that, supposing that such hypothesis were to explain such general propositions, we ought, in accordance with the common way of following all sciences, to admit it till some better hypothesis be found out.

(A Letter to Asa Gray from 20 July 1856; in: (F. Darwin 1887, vol. 2, pp. 78f.), italics are mine)

He wrote the same thing a few years later in a letter to William Wallace, this time about his highly controversial pangenesis hypothesis, which he himself described in his autobiography in: (F. Darwin 1887, vol. 1, p. 93) as “well abused”:

“My dear Wallace. You cannot well imagine how much I have been pleased by what you say about “Pangenesis” … What you say exactly and fully expresses my feeling, viz. that it is a relief to have some feasible explanation of the various facts, which can be given up as soon as any better hypothesis is found. It has certainly been an immense relief to my mind; for I have been stumbling over the subject for years, dimly seeing that some relation existed between the various classes of facts. ….”.

(A Letter to Alfred R. Wallace from 27 February 1868; in: (F. Darwin 1887, vol. 3, pp. 79f.), italics are mine)

In defense of this hypothesis, C. R. Darwin (1868, vol. 2, p. 357) referred to William Whewell’s The Philosophy of Inductive Sciences, in which the latter asserts that even incomplete or partially false hypotheses can be useful to the development of science (Whewell 1840, vol. 2, p. 225). In turn, Darwin wrote in his autobiography (cf. F. Darwin 1887, vol. 1, p. 93) that the very possibility of linking (explaining) many hitherto dispersed facts by a hypothesis constitutes its scientific value since the adoption of such a hypothesis can lead to a better understanding of the facts and, consequently, to seeking and finding in the future its empirical confirmation.

Admittedly, Darwin confirms his commitment to empiricism in the same autobiography when he writes that “an unverified hypothesis is of little or no value” in science. However, this is not the empiricism of Herschel or Mill. For Darwin, actual verification of a hypothesis was not a necessary condition for a hypothesis to be considered empirical. For him, a sufficient condition for the empirical character of a hypothesis was the possibility of the future confirmation of the hypothesis by new, yet unknown, facts:

Towards the end of the work I give my well-abused hypothesis of Pangenesis. An unverified hypothesis is of little or no value; but if anyone should hereafter be led to make observations by which some such hypothesis could be established, I shall have done good service, as an astonishing number of isolated facts can be thus connected together and rendered intelligible.

(Autobiography, in: F. Darwin 1887, vol. 1, p. 93)

Similar views on the empirical nature of the hypothesis were propounded by William Whewell (see Weber 2000, p. 173).41 As is well known, future developments in science and the philosophy of science proved Darwin, rather than Herschel, right. By the middle of the 20th century when the encyclical was published, all biologists and even some neo-scholastic philosophers were already adopting a very similar interpretation of the evolution hypothesis.42 According to the neo-scholastic philosopher Dondeyne (1951, pp. 14–15), mentioned above (see Section 3.1 and Section 3.2, note 25), at that time, none of the biologists, including those close to the Church, regarded the theory of evolution as “a fact that can be established directly”, as the encyclical demanded, nor did they believe that it could be “verified” definitively by facts. On the contrary, all agreed that it was “only” a hypothesis, but not just any hypothesis, rather an “eminently plausible” and “verifiable in its many consequences”, hypothesis that “cannot be rejected without being replaced by another one, at least as plausible”. As such, it was universally accepted by scientists, according to Dondeyne, as the best available explanation of empirical data, certainly better than the explanation based on the idea of “successive creation”.43

But in the 19th century, the idea of the usefulness in science of an unproven or even partially false hypothesis seemed difficult to accept from the point of view of conservative empiricism, and even more so from the point of view of methodologically conservative neo-scholasticism. The inertia of philosophical ideas often causes philosophy to lag behind the development of science and its method. Empiricism made concessions to unverified hypotheses only in the 1930s (cf. Carnap 1936, pp. 427f.).44 The official neo-scholasticism of the Catholic Church in the person of Pius XII in the mid-20th century was ready to accept the empiricist ideal of demonstrated and verified knowledge but was, apparently, not ready to recognize the scientific value of unverified but only well-confirmed hypotheses, even though at that time, this was already an idea widely accepted by scientists and by some neo-scholastic philosophers.

4. John Paul II’s Address

4.1. Historical Background

Our last text is John Paul II’s Address to the Plenary Session [of the Pontifical Academy of Sciences] on “The Origins and Early Evolution of Life” (John Paul II, 22 October 1996). This is an official speech, the original of which was written and presented in English (John Paul II 1996) and translated into the Vatican’s three other official languages, Italian, Spanish, and French, but only the French version was published in Acta Apostolicae Sedis (AAS vol. 89 (John Paul II [1996] 1997), pp. 186–90). The differences between these various language versions are worth highlighting and will be examined below. The text is devoted almost entirely to the question of the theory of evolution since this was the theme of the assembly of the Pontifical Academy of Sciences (PAS).45

This text, unlike the other two, does not require a broader discussion of the methodological context of its origins in order to be understood. However, a few important facts should be mentioned here. Firstly, it was the Second Vatican Council, held in 1962–1965, which changed, albeit not radically but at least profoundly, the Catholic Church’s attitude toward the modern world, including science and technology (see Kozhamthadam 2007). The main lines of this change are to be found in the Constitution on the Church in the Modern World Gaudium et Spes (AAS 58 (Gaudium et Spes [1965] 1966), henceforth as GS with section number), which expresses a profound desire to adopt a dynamic worldview in place of the static Aristotelian one, not without the influence of the idea and theory of evolution (see Kozhamthadam 2007, pp. 617f.). The Archbishop of Krakow, Karol Wojtyła, the future Pope John Paul II, was involved in the preparation of Gaudium et Spes (see Newton 2008, p. 389). The Constitution twice affirms the idea of the legitimate or rightful autonomy of science (GS 36 and 59) and deplores cases in which this autonomy has not been sufficiently respected, as in the case of Galileo, thus reinforcing the belief that faith and science are mutually opposed (GS 36). Another important contribution of the Second Vatican Council to the relationship between science and religion was the adoption of a new approach to the interpretation of Scripture, taking into account recent developments in the hermeneutics (see Dei Verbum, AAS 58 (Dei Verbum [1965] 1966), esp. sct. 12). This new approach to biblical interpretation is an important aspect of John Paul II’s speech (see John Paul II 1996, sct. 2).

Another important fact that should be mentioned here is John Paul II’s (Karol Wojtyła) interest in the relationship between science and religion while he was still Archbishop of Kraków in the 1960s and 1970s (cf. Russell et al. 1990, p. v; Trombik 2019, pp. 275–78). He continued the meetings he initiated in Kraków for many years as Pope in Castel Gandolfo (see Russell et al. 1993, pp. 1f.). This tradition was certainly an important factor in his commitment as Pope to the relationship between science and religion. His Message of 1 June 1988 to George Coyne, S.J., Director of the Vatican Observatory, on the relationship between science and religion (John Paul II [1988] 1989]) was widely echoed in the scientific and philosophical world. His approach has been called “the new vision from Rome” (Russell et al. 1990), and “the first major Pontifical statement on science and religion in three decades” (Russell et al. 1993, p. 2).

Inspired by the Pope’s statement, George Coyne proposed that a series of five conferences be organized over a decade by the Vatican Observatory and the Center for Theology and the Natural Sciences in Berkeley, USA. The common theme would be Scientific Perspectives on Divine Action. The third conference was held in Castel Gandolfo in June 1996. The theme was Molecular and Evolutionary Biology. John Paul II sent a cordial greeting to the participants of the conference, in which he expressed his appreciation for the whole series of conferences as “an important contribution to that exchange between religion and science which I have made every effort to promote since the first days of my Pontificate” (see (Russell et al. 1998, p. 1); originally, the text was printed in L’Osservatore Romano, 29 June 1996; the italics are original). This conference was not directly linked to the meeting of the Pontifical Academy of Sciences, but the topics were virtually the same. Moreover, John Paul II addressed both events, and his Address to the Pontifical Academy of Sciences was included, along with his Message to the conference, in the publication that followed the conference (Russell et al. 1998).

4.2. “Address” and “Humani Generis”: Methodological Comparison

In a manner typical of pontifical documents, the Pope refers to the declarations of his predecessors, in particular Pius XII’s Humani Generis. In an equally typical manner, he emphasizes the positive contribution of Pius XII to the explanation of the problem of the theory of evolution from a theological point of view and omits questions that might have been considered more controversial, implicitly enclosing them in the common category of the different state of scientific and theological knowledge at the time the encyclical was written.

From our point of view, what matters most is the statement on the theory of evolution, which takes into account the changed context of the development of science, philosophy, and theology. The Pope writes:

“4. […] Today, almost half a century after the publication of the Encyclical, new knowledge has led to the recognition of more than one hypothesis in the theory of evolution. It is indeed remarkable that this theory has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge. The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favour of this theory.

What is the significance of such a theory? To address this question is to enter the field of epistemology. A theory is a metascientific elaboration, distinct from the results of observation but consistent with them. By means of it a series of independent data and facts can be related and interpreted in a unified explanation. A theory’s validity depends on whether or not it can be verified; it is constantly tested against the [new] facts; wherever it can no longer explain the latter it shows its limitations and unsuitability. It must then be rethought.

Furthermore, while the formulation of a theory like that of evolution complies with the need for consistency with the observed data, it borrows certain notions from natural philosophy.”

(the italics are mine)

The first sentence of the above quote is the most confusing as it reads differently in English and in the three official translations. The English original, which speaks of “more than one hypothesis”, suggests the coexistence of different hypotheses of evolution, for example, empirical and philosophical. The Pope explicitly affirms this a few sentences later (Section 4) when he writes:

to tell the truth, rather than the theory of evolution, we should speak of several theories of evolution. On the one hand, this plurality has to do with the different explanations advanced for the mechanism of evolution, and on the other, with the various philosophies on which it is based.46

In contrast, all three translations say “more than [just] a hypothesis” (Spanish and French) or “more than a mere hypothesis” (Italian).47 The translations thus suggest the interpretation according to which the theory of evolution already has a scientific status beyond that of a mere hypothesis and, therefore, may have some theological implications. Both possibilities are interesting, but it seems that the original intention has been rendered in English although the version present in the translations is also supported by the following sentences giving a methodological interpretation of the theory of evolution and an argument from convergence in its favor.48

The English version shows that the Pope was aware of the current problems of the empirical theory of evolution, at least in the most general terms. It is hard to say who might have been the source of this information. The fact is, however, that at the Castel Gandolfo conference mentioned above, only Paul Davies rejected Darwinism and its idea of natural selection, while the other authors defended neo-Darwinism (see Russell et al. 1998, pp. 151–62). However, in the collection of texts published after the conference, we find a text by Ian Barbour that gives an overview of the many empirical positions known at the time regarding the mechanisms of evolution (Barbour 1998, pp. 420–24). As Barbour notes, the neo-Darwinian synthesis struggled from the beginning to explain many facts, and there were various attempts to “extend” it and to include additional factors responsible for evolution. He also discusses several views “beyond Darwinism”, like for example the idea of epigenetic factors. He states that, although these ideas are “controversial and outside the mainstream of the current biological thought, they should not be dismissed if they are able to account for observed phenomena more adequately than neo-Darwinian theory” (ibid., p. 423).

We do not know if this was the source of the Pope’s knowledge, but these ideas were certainly present at the time in the Holy See offices that prepared the texts for the Pope. And such an awareness of the many possible empirical solutions to the problems of the current theory of evolution could only encourage the methodological statements present in the Address, especially the idea of the hypothetical and temporal nature of the scientific theories.

The methodological language in the Address is closer to the methodology of Darwin than that of the encyclical Humani Generis. Admittedly, the empiricist expression “verification” appears in it, but one can infer from the context that it does not mean definitive verification, i.e., positive confirmation of a theory by all facts that can be deduced from (predicted by) that theory, but confirmation by successive new facts. More significant and more “Darwinian” is the general methodological statement that the accumulation of facts that are inexplicable on the basis of a given theory consequently leads to the need to revise and modify it (“It must then be rethought”). According to the Address, the theory of evolution, like any other empirical theory, is subject to constant testing by new empirical facts with which it must be consistent, and it is possible that over time, under the pressure of facts incompatible with it, if any, it will be replaced by another, better theory.

We know that this methodological idea of the constant need to replace old scientific theories with new ones, typical of Darwin, struggled to gain acceptance among empirically-minded scientists and philosophers during his lifetime. Nevertheless, it had already become an integral part of the self-awareness of scientists at the turn of the 19th and 20th centuries.49 However, it was not until a century later, with John Paul II, that it became part of the methodological landscape of official Catholic theology. For Pius XII, defending neo-scholastic philosophy, such an idea must have appeared as another manifestation of the idea of universal evolution leading to the negation of immutable and perennial truth. As we know, he rejected this idea in Humani Generis (HG 5).50

Another argument in favor of the “Darwinian” methodology of the Address is that it does not require proof or demonstration of the theory of evolution through facts. On the contrary, the text allows for the methodological idea that scientific knowledge likely to have theological implications can be hypothetical in nature. Consequently, the Pope acknowledges that the theory of evolution remains a hypothesis but, nevertheless, considers it already capable of influencing theology while still excluding the spiritual soul or the human person from this influence. It is true that the translations imply, as we noted above, the recognition of the theory of evolution as something “more than a mere” hypothesis. But in so doing, they tacitly assume that the concept of a scientific hypothesis is subject to gradation and that only a pure (mere) hypothesis unsupported by facts cannot be taken into account by theologians. This, however, is not the case with the hypothesis of evolution. According to the Address, it is strongly supported by empirical science.

The author of the Address finds sufficient confirmation in the “convergence” of evolutionary ideas in varied and often distant scientific fields. The process, which has been observed in science for a long time, of independent confirmation of the effectiveness of the idea of evolution in explaining different areas of reality and in different fields of science testifies in favor of its credibility:

It is indeed remarkable that this theory has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge. The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favour of this theory.

(John Paul II 1996, sct. 4)

This argument bears all the similarities of William Whewell’s “consilience of inductions” or “coherence argument”. According to this argument, the capacity of an idea (cause) to explain an increasingly broad class of phenomena, often initially remote from one another, is strong support for the correctness of the idea or cause put forward (see Snyder 2023, part 3). It was also one of Darwin’s arguments in his On the Origin of Species (C. R. Darwin 1859, pp. 4, 129, 152, 264, 266, 453, 478) for the superiority of the explanation of biological change by natural selection over other explanations, especially the theory of creation.

It is also worth noting that, while Humani Generis was written with the intention of condemning the idea of universal, cosmic evolution, John Paul II recognized the universality of the idea of evolution in the various sciences as a confirmation of its soundness.51

Once again, the difference between the English and Italian formulations is significant here. The English text speaks of the capacity “to explain new facts”, while the Italian translation uses the traditional phrase “dimostrata dai fatti” (demonstrated by facts). However, it seems that this translation does not necessarily mean demonstration in the strict sense but only empirical confirmation by new facts. The English text also uses more contemporary methodological language than any of the translations when it speaks of the continuous testing of a hypothesis against facts.52

Philosophy and Science

Another methodological novelty of John Paul II’s text in relation to his predecessors is also his reference to contemporary anti-positivist interpretations of the relationship between philosophy and the empirical sciences,53 distinguishing but not separating the empirical level of scientific theory from its philosophical aspect. Indeed, he asserts that the theory of evolution is not limited to the level of facts but, also, refers to certain philosophical ideas from the field of natural philosophy.54 This distinction can be linked directly or indirectly to one of the currents of 20th-century neo-scholasticism, which believed that neo-scholastic natural philosophy could and should be taking into account the achievements of empirical sciences (see d’Amore 1948a, 1948b, 1949).55 According to this strand of neo-scholasticism, natural philosophy derives philosophical implications from science according to its own philosophical method and principles.56

The expressions in the Address are ambiguous in this respect, probably deliberately so that the text cannot be linked to any particular philosophy or philosophical concept. For example, the Pope writes that “empirical explanations of the mechanism of evolution” are “based” on various philosophies (n. 4).57 Contemporary approaches to philosophy in science tend to avoid the traditional idea of a foundation or basis for philosophical assumptions in science, if any. Rather, a distinction is made between the empirical aspect of a scientific theory and its philosophical implications or interpretations. But the text does not necessarily mean foundation in the sense of scholastic philosophy, which treated metaphysics this way in relation to physics. At the end of the Section 4, the following conclusion is given:

Hence the existence of materialist, reductionist, and spiritualist interpretations. What is to be decided here is the true role of philosophy and, beyond it, of theology.

Ultimately, the Pope does not pretend to prejudge methodological issues but calls for a discussion on the role of philosophy and theology in the context of theory of evolution, and scientific theory in general.

In the following Sections 5 and 6, the Pope addresses both theological and philosophical problems of the uniqueness of man as a person in relation to the rest of the biological world. He, thus, means the same thing that Pius XII had in mind in Humani Generis when he wrote that the human soul is not subject to the laws of biological evolution but comes directly from God. John Paul II, too, denies the possibility of fully explaining the origin of man—as a person unique in God’s eyes and endowed with a mind—based on the empirical mechanism of the theory of evolution alone. The Pope rightly believes that no empirical facts can resolve between the materialist interpretation and the Christian interpretation of the theory of evolution and that philosophical analyses are needed in this regard.58

We can, therefore, consider that the text of the Address represents a further but not final methodological step in separating in official texts the empirical aspect of the theory of evolution from its philosophical interpretations. Such a separation seems to be a necessary step for a more objective approach of theology to scientific theories and for avoiding their hasty rejection on purely philosophical grounds as it happened in the past and led to the deplorable idea of a conflict between science and Catholic theology (cf. GS 36).

5. Methodological and Epistemological Conclusions

On the basis of the historical analysis, I will now attempt to answer the questions posed at the outset.

In principle, all three texts admit the possibility of the influence of non-theological science on theology. Bellarmine, in his letter to Foscarini, admits the possibility of a situation in which Copernicus’ theory would force a change in the interpretation of Scripture, although he personally doubts that this would ever happen. Pius XII, in Humani Generis, also admits such a possibility with regard to the theory of evolution, but only with regard to the evolution of the human body, whereas he excludes such a possibility with regard to the spiritual dimension of man, i.e., the human soul. John Paul II’s position is essentially similar in this respect. He repeats the words of Pius XII, with one difference. He puts more emphasis on the dignity of the human person than on the spiritual soul.

The questions we are to answer concern the methodological criterion that a scientific theory must meet in order to have theological implications, according to our authors. First of all, we need to know what it is. Then, whether it is the same or different in all three cases and whether it is a question of methodological continuity or lack thereof. Only after these questions have been answered will it be possible to draw conclusions about the last issue, namely, the nature of the relationship of Catholic theology and the methodology and epistemology of non-theological sciences: to what extent it is or may be dependent on, and to what extent it is independent of, the current state of the methodology of science in choosing one or another criterion of theological acceptability of scientific theories.

5.1. Methodological Criterion: Demonstration vs. Hypothesis

At the outset of my historical analysis, I identified the two key methodological terms of “demonstration” and “hypothesis” as they appear in all three texts, which can, therefore, be used to analyze these texts and answer the questions posed. In line with this assumption, my response will refer to these concepts.

As we have seen, Bellarmine and Pius XII believe, explicitly or implicitly, that only demonstrated knowledge can influence and imply changes in theology. This idea is present in the notion of demonstration as well as in the notion of hypothesis, both of which they use. A hypothesis that has not been demonstrated cannot be taken into account by theologians in the process of forming theological positions. A demonstration and hypothesis are, therefore, two sides of the same criterion for accepting a scientific theory as locus theologicus. In both cases analyzed, the existence of a demonstration is considered a necessary and sufficient condition for acceptance. Likewise, in both of them, being a hypothesis implies the lack of demonstration and, consequently, the lack of acceptance.

The lack of demonstration undermines the theological ambition of the Copernican hypothesis in Bellarmine’s eyes. Similarly, the lack of demonstration for Darwin’s hypothesis results in Pius XII’s appeal to theologians and scientists to exercise the utmost caution with regard to the hypothesis and to refrain from accepting it definitively while being willing to submit to the final judgment of the Church’s Magisterium.

However, and it is significant and worth emphasizing here—moving somewhat away from the main issue—that in both cases the affirmation of the lack of demonstration and of the hypothetical nature of the theory was not absolute but only temporary. Both Bellarmine and Pius XII accepted, in principle, the possibility that the methodological status of these theories might change in the future provided that the necessary demonstrations appeared.

This attitude may have had its justification in Aristotle’s logic, according to which only perfect demonstration gives ultimate certainty in science and leads to a state of “contemplation” of the truth, without the need to seek it further. The mere lack of demonstration cannot provide such certainty, so there must always remain the possibility of finding an adequate demonstration in the future, hence the fundamental openness of Aristotle’s logic to the constant search for adequate demonstrations. If there was a true demonstration that, for example, Darwin’s theory is false, there would be reason to reject it altogether. We also know that many theologians considered the assertion of a theory’s philosophical absurdity to be such a demonstration. This was one of the reasons why Copernicus’ theory and Galileo himself were condemned in 1616 (see Fantoli [1994] 1996, p. 216). The consultors of the Holy Office very quickly agreed on their position regarding the two Copernican theses defended by Galileo, namely, that the Sun is motionless at the center of the world and that the Earth moves both in relation to the whole system and in diurnal motion. They stated, among other things, that both of these propositions are “foolish and absurd in philosophy.” In doing so, they also had confirmation from an authority, Ptolemy’s Almagest (see Giostra 2015, p. 260).59 A similar qualification was attributed to the theory of evolution by some Holy Office consultors in the 19th century(cf. Artigas et al. 2006, p. 84).60 Pius XII was much more cautious in this respect, despite the pressure from the College of Cardinals.61

A somewhat different and more natural justification for this attitude can be found in a text that is extremely interesting from this point of view, although it may be seen as highly controversial, even arrogant, by some. This is the text of the theologian Henri Marrou, who, in 1950, in the French periodical L’Esprit, undertook a defense of Pius XII against the accusations of scientists who defended the scientific status of the theory of evolution against his Humani Generis:

The fact that the evolutionary hypothesis imposes itself with a kind of practical necessity on all the biologists and geologists of our time, is not a sufficient reason for what remains in the eyes of theologians a strictly logical and simple scientific hypothesis to impose itself with enough authority to force them to readapt a traditional exegesis. Their attitude scandalizes many—so much so that this evolutionary conception of the world has become a normal form of thought, for the men of our time as much as for our scientists. Yes, but in twenty centuries of history, the Church has already seen so many Weltanschauungen, by turns as “necessary” and outmoded …

We can fully appreciate the gap that separates the peaceful autarky of the Catholic theology, which, sure of itself and its future, asserts itself majestically, seemingly indifferent to the changing fashions of the spirit (of which it nevertheless knows, with the necessary delay and hindsight, how to assimilate every contribution).

(Marrou 1950, p. 566; translation and italics are mine)

For Marrou, the Church operates in a much longer perspective than modern science. It cannot, therefore, be too concerned with current scientific and methodological fashions since its primary task is to protect the faith from an error.

However, particular attention should be paid to the second part of this quotation. Indeed, over a sufficiently long period of time and with guaranteed freedom of thought, the Church and its theology end up assimilating everything that proves correct in science over time. This is an example of Catholic theology’s “relativization” of historical scientific theories.62 It is also clear from this text that by the middle of the 20th century, the Church’s mentality had not yet been able to fully assimilate the modern idea of scientific progress.

It can only be assumed that similar motives guided Pius XII in Humani Generis, both when he urged theologians and scientists to exercise the utmost caution in addressing the question of the evolution of the human body and when he decided, against the pressure from the cardinals, not to clarify the text on the question of monogenism. Unlike his future successor, John Paul II, Pius XII showed little interest in the sciences, following the principle of peaceful autarky of Catholic theology articulated by Marrou.

But let us return to the main problem, namely, the question of the criterion for the theological acceptability of scientific theories. In his text, John Paul II adopts a different methodological position from that of Bellarmine and Pius XII. He does not require a demonstration of the theory of evolution before it can influence theology. At least, the original English text contains no such term. Unlike previous texts, according to the Address, hypotheses that have not been demonstrated can also have an important theological significance. However, the lack of a requirement for demonstration does not imply the lack of any methodological condition. This condition is implicitly expressed in the form of the convergence argument adduced in favor of the plausibility of the evolution hypothesis. This shows that John Paul II’s text adopts a much weaker criterion than a demonstration. This criterion can be expressed in general terms as a sufficient confirmation or sufficient recognition of the hypothesis within the empirical sciences themselves and removing reasonable doubts.

The absence of a demand for a demonstration in John Paul II’s text is not the only methodological difference between the three texts. Another difference, and perhaps even more significant, is revealed in the different meanings that Bellarmine and Pius XII give to this term in their texts. Bellarmine understands by the required demonstration a perfect demonstration in terms of Aristotle’s logic, that is, a syllogistic demonstration from the first premises by means of a direct efficient cause or at least something similar if Baldini’s interpretation is correct (see Section 2.2 above). Pius XII, on the other hand, understands by demonstration either Aristotle’s imperfect demonstration from effects or from signs or, more likely, empirical verification by facts, i.e., a demonstration in the sense of 19th-century empiricism.

An analogous difference is apparent in the use of the term “hypothesis”. Indeed, all three texts oppose hypothesis to scientific knowledge; nevertheless, only Bellarmine excludes hypotheses from the field of science altogether. Pius XII speaks of hypotheses having some scientific basis. John Paul II, on the other hand, fully recognizes the idea of a scientific hypothesis lacking a final demonstration.

Thus, in the case of Bellarmine and Pius XII, we are dealing with a different methodological interpretation of the apparently identical criterion for the acceptability of scientific theories as locus theologicus, which was the criterion of demonstrated knowledge as opposed to hypothetical opinion. In the case of John Paul II, the criterion is tempered and becomes that of a sufficiently justified hypothesis.

So can we still speak of methodological continuity in the Church’s position? Terminology itself can be misleading, creating the appearance of continuity or discontinuity. However, anyone with even a superficial knowledge of the hermeneutics of historical texts will not look for such continuity at the level of terminology, but at the level of the concepts and ideas behind the terminology.

5.2. Methodological and Epistemological Continuity or Discontinuity?

The question arises as to whether there is anything (or anyone) that could bring all three texts together from the methodological point of view. It seems appropriate at this point to ask about the common source of the idea of the demonstration requirement as a criterion for the theological acceptability of scientific hypotheses. According to Ernan McMullin (2013), this requirement was first formulated by Saint Augustine in antiquity. Significantly, both Bellarmine and Galileo invoked Augustine when talking of the necessity of demonstration; or, more precisely, they referred to the methodological conditions he formulated mainly in De doctrina christiana (On Christian Doctrine) and De Genesi ad litteram (The Literal Meaning of Genesis). The same conditions were evoked much later, at the end of the 19th century, by Pope Leo XIII (1893) when he wrote an encyclical “Providentissmus Deus” on the principles of the interpretation of Scripture, including in the face of new scientific theories. In turn, the text of Leo XIII was invoked by both Pope Pius XII (1950, sct. 2) and John Paul II (1996, sct. 2), quoting the words that “truth cannot contradict truth”, a sentence inspired by the sayings of Augustine.

I will briefly outline the methodological conditions formulated by Augustine under which pagan philosophy (science) can force a reinterpretation of Scripture. As we will see, with their help, it is very easy to interpret all three texts and, at the same time, to identify the common element linking the three different approaches to the methodological criterion. Basically, I will use here the results of McMullin’s (1998, pp. 291–99; 2013) analysis, expanding and supplementing it using direct references to Augustine’s texts.

Augustine’s statements referred to pagan philosophy. In antiquity, philosophy was commonly identified with all scientific, non-Christian knowledge.63 Ancient Christianity had to meet the intellectual challenge of encountering the omnipresent Greek philosophy. The distinctive feature of Augustine’s thought was his recognition of the relative autonomy of philosophy (or science) in relation to the Christian faith when it came to the knowledge of the world. He admitted that pagans, thanks to their philosophy, could know the world better than Christians and that it would, therefore, be a disgraceful and dangerous thing if Christians held to a literal interpretation of Scripture against true philosophy (cf. Augustine 1845, p. 261 (I, XIX, 39); 1982, vol. 1, p. 42). Augustine thus ruled out the separation of Christian theology from philosophy (science), and accepted the possibility of reinterpreting theology under the influence of philosophy. He thus gave a positive answer to the question: “Can science influence Christian theology?” Augustine’s position, if not immediately, at least from the 12th century onward, played a major role in the self-perception of Christian theology. The same was true of Bellarmine and the Holy Office in Galileo’s day.64

McMullin identified seven principles in Augustine, some of which are methodological and epistemological in nature and can be used for a comparative analysis of our three cases. The others are eminently theological in nature.

The first principle is called by McMullin (2013, p. 197) The Principle of Consistency. It is identical in meaning to the text of Leo XIII quoted above. St. Augustine in his On Christian Doctrine asserts that there cannot be two truths, philosophical and religious, but only one, since all truth comes from God (cf. Augustine 2009, p. 53).65 This principle places the entire discourse on the relationship between Christian theology and science (philosophy) in the realm of epistemology. It expresses the conviction that both disciplines pursue truth, which, as it comes from God, must ultimately be one—hence, the simple consequence. In theology inspired by Augustine’s principle, it is assumed by definition that there can be no real contradiction between scientific truth and the truths of faith. All contradictions are, therefore, apparent and must be capable of being resolved. They can only be the fault of someone who wrongly interprets words or things. However, this principle does not determine on whose side the error lies, whether it is on the side of science or the side of the interpreter of Scripture and the theologian.66 For that, additional conditions or principles are needed.

The next principle, or more appropriately three related principles, expresses the Augustinian understanding of the methodological criterion for regarding scientific (philosophical) theories as acceptable locus theologicus. The first is called by McMullin The Principle of Priority of Demonstration (PPD). According to it, the reinterpretation of Scripture is permitted and necessary only if secular science can provide a demonstration or proof of the truth of a thesis contrary to the claims of Scripture.67

Equally important is The Principle of Priority of Faith (PPF), according to which, in the absence of scientific proof, philosophical theses are to be considered invalid.68 The last of these three principles The Principle of Priority of Scripture (PPS) says that in the absence of a demonstration, a Christian should stick to the existing, usually literal interpretation of Scripture. According to McMullin, the last two principles constitute a kind of limitation on PPD.

It is not difficult to relate the PPD principle to Bellarmine’s or Pius XII’s demand for demonstration, as well as the PPF and PPF principles to the category of hypothesis, which excludes the possibility of accepting an idea or theory and forces adherence to the traditional interpretation of Scripture and theology.

But only in appearance do Augustine’s principles seem identical to those of Bellarmine and Pius XII. Both of these authors were associated with a particular philosophy that imposed on them a particular understanding of a “demonstration”. Augustine, for his part, cannot be linked to any specific logical or methodological tradition. As we know, in Augustine’s time, the Latin world knew very little, if anything, of Aristotle’s logic. Plato’ logic did not exist either, and Stoic logic had fallen into oblivion at the time (cf. Bobzien 2020). Augustine’s understanding of scientific knowledge and demonstration was a matter of common sense.

When speaking of demonstration (demonstratio), Augustine (1845, p. 91 (n. 6)) referred to reasoning (ratiocinatio) on the basis of true and credible arguments or evidence, which he systematically called “documenta”.69 The opposite of reasoning on the basis of documenta for Augustine was an empty rhetoric of a sophisticated and seductive discourse.70 Documenta could be of different kinds. They could be passages from Scripture, rational arguments, observational arguments (Augustine 1845, p. 232), empirical analogies (ibid., p. 239), and even signs pointing to the existence of God (ibid., p. 1063).

For Augustine, not all “documenta” were worthy of belief. Speaking of demonstrations involving the need to reinterpret the text of Scripture, Augustine demanded that they be trustworthy or reliable (ibid., p. 262) and, above all, that they prove the truth beyond all doubt:

But if, by chance, they were able to prove it with such arguments (talibus documentis) that there could be no further doubt (ut dubitare inde non debeat), then it must be shown (demonstrandum est) that what we said about the skin does not contradict these true reasons.

(ibid., p. 271)71

Augustine refers to the criterion of truth widely accepted since antiquity, namely, intellectual evidence or certainty identified with indubitability. This is certainly linked to Augustine’s use of the term “demonstratio”. This term has its origin in the term “monstrare”, which means to show visually, point out, indicate, and only secondarily, in Aristotle’s logic, it takes on the technical meaning of necessary demonstration but only because it shows perfectly and undoubtedly the truth.72 In antiquity, the metaphor of seeing something clearly meant also intellectual, noetic cognition, not subject to further doubt.

However, as the two criteria given by Augustine—“demonstratio” and “indubitability”—have no precise meaning linked to a specific logic, their understanding is subject to change, depending on the fluctuating context in which they occur.

Each of the authors we have analyzed applies the Augustinian criterion of demonstration in the sense that is consistent with the meta-scientific paradigm they believe to be in force. Bellarmine and the theologians of the Holy Office interpreted Augustine’s term according to the paradigm of Aristotle’s episteme (scientia) and in its most conservative form. Galileo, for his part, interpreted Augustine according to a different understanding of the Aristotelian paradigm that had emerged in the circles of natural philosophy in Padua. He saw his dimostrazioni necessarie, i.e., demonstrations from effect or sign transformed into regressus, as sufficient to force a change in theology. Hence the “inter-paradigmatic” disputes with Bellarmine over the notion of true demonstration.

Pius XII’s encyclical was intended as a defense of neo-scholastic, i.e., essentially Aristotelian, philosophy, but it also drew on non-Aristotelian methodological standards developed in 19th-century empiricism, which must have coincided sufficiently with Aristotelian standards to allow them to be identified, at least in some respects.

As for the text of John Paul II, the mere absence of the term “demonstration” in his text does not invalidate the possibility of linking this text to Augustine’s criterion. It can be assumed that he also referred to the PPD principle, except that he understood it in accordance with the methodology of science in force at the end of the 20th century. The only possible understanding of the postulate of demonstration or proof in this new perspective is to demand the strongest possible available justification, one that removes all reasonable doubts.

In explaining these differences in the application of the Augustinian principle of PPD, it may also be useful to refer to the idea of textual hermeneutics. From this point of view, the interpretations of Bellarmine and Galileo should be considered an uncritical and ahistorical attempt at a literal reading of Augustine’s criterion. Awareness of the need for textual hermeneutics did not exist in their time. In the case of Pius XII, there is no such certainty; nevertheless, his simultaneous defense of neo-scholastic philosophy and appeal to a different meta-scientific paradigm when evaluating the theory of evolution suggests a lack of sufficient criticism and awareness of this situation.

The case of John Paul II is different. The text shows that he had a much greater awareness of the principles of textual hermeneutics than previous authors, and probably not just of the biblical text but of any text (cf. John Paul II 1996, sct. 2). Thus, his awareness of the principles of hermeneutics may have led him to recognize that the Augustinian criterion requires a critical reading and adaptation to the contemporary paradigm of scientific knowledge. In this perspective, his statement is an interpretation of Augustine’s criterion from the point of view of the modern paradigm of scientific knowledge, in which the notion of demonstration in the literal sense has lost its meaning in the empirical sciences, retaining its validity only in the mathematical sciences.

So, if we apply the hermeneutical principles of interpretation to our historical texts and rid them of context-dependent interpretations, we can distinguish a core element of Augustine’s criterion that remains common. Scientific, non-theological knowledge must be justified in such a way as to remove reasonable doubts as to its truth or validity. In other words, it cannot be a mere, fanciful hypothesis of the human mind but must be sufficiently tested or confirmed.

5.3. Methodological Dependence or Independence?

A final question remains to be answered, namely, whether Catholic (or more broadly Christian) theology, in establishing criteria for the recognition of scientific theories as capable of modifying theological formulations, can be independent of the methodology of the non-theological sciences. This latter question needs to be differentiated between its factual aspect, i.e., how the authors studied and acted, and its general and normative aspect.

In the three cases studied, the authors were determined by the methodological paradigm they chose. Their methodological ideas were derived from the theory of knowledge at their disposal. From this point of view, it is difficult to speak of independence.

But we have also seen that Bellarmine refused to accept Galileo’s methodological perspective, and Pius XII refused to accept Darwin’s methodological perspective. At least from Galileo’s time onward, the coexistence of two or more distinct methodological paradigms was a historical fact. And the theologian could choose between them whichever he considered best suited to his theological requirements. This is where there is room for limited or relative independence.

The question arises, of course, about the criteria for such a meta-methodological choice. Usually, it has been a conservative principle of caution or prudence.73 It was emphatically expressed by Henri Marrou (1950), quoted above (see Section 1 in this chapter). According to him, the Church is only “seemingly indifferent” to sciences and their methodologies, that is, only in the short term. In the long run, however, it is able to assimilate from changing sciences and ideological fashions all that has turned out to be long-lasting. Longer perspective and lack of haste are other names for caution or prudence, necessary in the case of truths of faith that cannot undergo as rapid changes as scientific and philosophical ideas.

The conservative methodological principle of prudence found in theology can be formulated as follows: choose the strongest available criterion for the acceptability of scientific theories in order to best protect the deposit of faith.74 This is what Bellarmine did, and this is also what Pius XII did. As it seems, John Paul II also followed an analogous, albeit less conservative, precautionary principle when he considered the argument from convergence as sufficient and the strongest available, i.e., philosophical, argument in favor of the theory of evolution.75

The analysis of our three texts thus leads to the statement of the relative or non-absolute independence of official theology from the methodology of non-theological science.

The general answer will be slightly different, and can only be hypothetical, i.e., it must take the form of a conditional “if … then”. First of all, the antecedent of such an answer must include an answer to the question of whether the non-theological sciences can influence Christian theology. The history of Christian thought teaches us that there have been instances of total denial of such a possibility. This position is attributed to many of the early Church Fathers and the supporters of the idea of contempt for the world (contemptus mundi). In the 20th century, the representative of such a negative position, albeit for quite different reasons, was one of the two schools of neo-Thomism, whose most famous exponent was J. Maritain. This school proclaimed the independence of scholastic philosophy and, also, of scholastic theology based on this philosophy from the empirical sciences since they move on two ontological and methodological levels that do not intersect: the essences of things and phenomena. From this perspective, theology and the philosophy that serves it can learn nothing from the empirical sciences as such.76 With such an antecedent, the consequent can only be one: theology is entirely independent of the methodology of the empirical sciences.

However, if, in the spirit of St. Augustine, theology accepts a positive answer, the general answer will be similar to the factual answer: theology can only be relatively independent of the methodology of science. Theology itself does not develop the methodology of science but must draw it from philosophy. What remains is the autonomy of choice between the different methodologies available. Adopting a more conservative position means opting for an older methodology that has been well assimilated by existing theology. With a less conservative approach comes the obligation for theologians (see John Paul II 1996, sct. 3) to keep up to date with current developments in empirical science and meta-science in order to adapt new developments to the requirements of faith.

Still, another answer can be reached by using different time perspectives. In the short historical perspective of a particular theologian, especially one who occupies an official position in the Church’s Magisterium, his independence from the methodologies of the sciences is relatively small since the principle of conservative prudence often prevents him from espousing the latest ideas. However, in the longer historical perspective of theology understood as a discipline subject to evolution over time, the relative independence of theology from specific methodologies will become more apparent. By rejecting older methodologies as superseded, theology can free itself from their limitations. Of course, it will always do so from inside a new, currently accepted methodological perspective. Nevertheless, having learned by experience, we need not treat it as definitive.

Agreeing to the essentially common-sense and, thus underdetermined, nature of the methodological criterion for the acceptability of scientific theories by theology is a guarantee of its relative independence from specific methodologies of science. At the same time, however, it forces it to be bound to some specific methodology, at least temporarily. If this is the case, theology that accepts Saint Augustine’s fundamental choice cannot avoid being influenced by changing conceptions of science and its methods. Thus, the methodology of science that provides theology with criteria for the acceptability or unacceptability of scientific theories as a locus theologicus itself becomes a locus theologicus that shapes theological positions. If we accept that scientific theories are an “objective” locus, concerning the object of theology, the methodology will, in turn, be a “meta-objective” locus concerning the criteria for the acceptability of scientific theories as an objective locus in theology.