Ontology, the most fundamental branch of metaphysics, is the study of being or existence as well as the basic categories thereof. A being is anything that can be said to 'be' in various senses of the word 'be.' 'Be' is a word, like many other words, that has different senses. So there are different senses of the word "be," and accordingly, one might say, there are different "kinds" of beings, or ways of being. In Aristotle's phrase, ontology is "the science of being qua being." The word 'qua' means 'with regard to the aspect of'. So ontology is the science of being with regard to the aspect of being--so it is the study of beings insofar as they exist. More precisely, ontology concerns determining what categories of being are fundamental or irreducible and asks whether, and in what sense, the items in those categories can be said to "be."
Here are examples of ontological questions:
- What sort of concept is existence?
- Is it possible to give an account of what it means to say that a physical object exists?
- What are physical objects anyway?
- What are an object's properties or relations and how are they related to the object itself?
- When does an object go out of existence, as opposed to merely changing?
There are, of course, many more.
Ontological problems and topics
The ontological problems par excellence include:
- What is Existence?
- Is Existence is a property?
- The Problem of universals
- The Problem of substance: Are Objects ultimately bundles of properties or instead Substance's?
There are, however, very many more ontological problems than these.
See also artificial intelligence for the specialized use of the word ontology: for applications within computers, specifically in an area known as knowledge representation, an ontology is a data structure containing all the relevant entities and their relationships within a domain. Computer programs can then use the ontology for a variety of purposes including inductive reasoning, classification, and a varety problem solving techniques. Typically, ontologies in computers are tied closely with controlled vocabularies.