**1. Introduction**

The field of applied ontology came to prominence in the 1990s [1,2], driven by knowledge engineering issues. In order to achieve coherent and shareable knowledge bases, engineers and scientists sought answers to questions in essence like "what is the meaning of a physical quantity?" [3] or "what exactly constitutes a gene?" [4]. The similarity to questions raised in philosophical ontology was readily apparent [5], opening up the possibility of joint engineering and philosophical ontology research.

Arguably, applied ontology is not merely the application of philosophy *to* other disciplines like engineering. Rather, the discipline also informs philosophy itself—at the very least by raising new questions about the existence of things, but hopefully also by novel approaches and answers to those questions. As such, applied ontology is one pathway in the journey of reconstituting a natural philosophy, in the sense of Dodig-Crnkovic and Schroeder's connected conceptual engineering [6].

The interaction with philosophical ontology is especially visible at the foundational ontology level. Foundational ontologies<sup>1</sup> deal with fundamental aspects of our world, such as "material objects", "events", "being part of" and so forth. They underpin ontologies of particular domains such as biomedicine or information systems [2,7] (pp. 115–139).

Currently, one of the most prominent foundational ontologies is the Basic Formal Ontology (BFO) [8]. BFO is a realist ontology, based on a relatively small set of universals and relations2. That is, BFO asserts that the (real) universe can be carved up into universals such as *objects*, *processes*,

<sup>1</sup> Also called "upper ontologies".

<sup>2</sup> BFO includes relations (as per the specification), but these are as ye<sup>t</sup> not included in the bfo.owl file. The discussion here refers to the specification.

*boundaries* and *qualities*. By "universals", BFO means " ... what all members of a natural class or natural kind such as a *cell*, or *organism*, or *lipid*, or *heart* have in common ... not only in the realm of natural objects such as enzymes and chromosomes, but also in the realm of material artifacts such as flasks and syringes, and also in the realm of information artifacts such as currency notes and scientific publications" [9] (p. 13). BFO has been successful in supporting engineering and scientific research in areas such as genetics, information systems and defence [10].

In previous work on the ontology of competitive intelligence [11], I developed a core ontology based on particularized relations, or *tropes*, which are fundamentally di fferent from the universals that BFO is based on (discussed in detail below). It is beyond the scope of this article to review the arguments for and against tropes (of which there are many flavors), su ffice it to say that tropes are prominent in ontological theory that addresses the nature and quantity of properties (like being "a chair" or "being red") [12]. At the applied level, tropes as particularized relations provide a way to connect causes to the structural relations that define entities, providing a seamless foundation for both entities and causality [11]. From either perspective, universals vs. tropes is a core ontological commitment.

The previous work compared the trope ontology to several other ontologies, but not BFO. Given the prominence of BFO, it is important for lesser known ontologies such as the trope ontology to provide at least some comparison, but preferably a "matching" to BFO. This is important because foundational ontologies often act as the "glue" to connect disparate domain ontologies and, if a matching is possible, it would link the trope ontology to the wider world of ontologies based on BFO. Moreover, given the subject matter of foundational ontologies, discussion of such matchings informs philosophical ontology—albeit with a constructive, rather than critical emphasis.

Matching is commonly defined as "the process of finding relationships or correspondences between entities of di fferent ontologies" [13] (p. 39). I include in this looking for points of similarity, where terms in one ontology can be coherently defined in terms of another. As such, "matching" reflects a perspectivist stance towards ontology. That is, it recognizes that di fferent ontologies may reflect di fferent aspects or viewpoints of reality (including perhaps some level of denial of that reality).

In summary, this article examines how the trope ontology was matched to BFO and what ontological insights we might obtain from such a matching. The next section will briefly outline the trope ontology and the remaining sections will match core terms of the trope ontology to BFO. In the conclusion, I will provide some general observations about the results of the matching and the relationship between the two ontologies.
