The Six Category Ontology

Modern-day analytical metaphysics embraces what we can think of as a two-category ontology (2CO) consisting of individuals/particulars on the one side and properties/attributes on the other. (Metaphysical nominalism, in these terms, can be described as a 1CO.) The 2CO ontology is motivated, in the work of some philosophers at least, by the bicategorial syntax of first-order predicate logic ('F(a)', 'R(a,b)', ...), and the philosophers in question -- Russell, Wittgenstein in the Tractatus, David Armstrong in some of his writings -- might thus be said to embrace a doctrine of 'fantology'.

E. J. Lowe's four-category ontology (4CO), which is a modern-day counterpart of Aristotle's ontological square, embraces a dichotomy of both substances and modes, on the one hand, and of universals and particulars, on the other.

Basic Formal Ontology (BFO) goes one step further than Lowe by accepting also an ontology of events (also called occurrents, processes). In this it follows Davidson's theory of actions and events, but goes beyond Davidson in accepting events at the level of both particulars. and universals.

[ODSD_EXCITEMENT]

I found this presentation to be enlightening in that it helps to gain mental models and thinking tools most useful when comparing TLO frameworks. Indeed one must understand the intrinsic capabilities of ontology framework you wish to use in trying to model knowledge that people and computers can reason about. These Ontology frameworks aren't equal and interoperability is not always possible. Great presentation.