Imported from Wikipedia on 2005-03-14
Ontology is a study of conceptions of reality and the nature of being. In philosophy, ontology (from the Greek ὤν: being, and -λογία: study) forms the basic subject matter of metaphysics. It studies being or existence and their most basic categories —trying to find out what entities and what types of entities exist. Ontology has strong implications for our conceptions of reality.
Some philosophers, notably of the Platonic school, contend that all nouns refer to entities. Other philosophers contend that some nouns do not name entities but provide a kind of shorthand way of referring to a collection (of either objects or events). In this latter view, mind, instead of referring to an entity, instead refers to a collection of mental events experienced by a person; society, instead of referring to an entity, refers to a collection of persons with some shared characteristics; and geometry, instead of referring to an entity, refers to a collection of a specific kind of intellectual activity.
As a philosophical subject, ontology chiefly deals with the precise utilization of words as descriptors of entities or realities. Any ontology must give an account of which words refer to entities, which do not, why, and what categories result. When one applies this process to nouns such as electrons, energy, promise, happiness, time, truth, causality, and god, ontology becomes fundamental to many branches of philosophy.
Ontology has one basic question: "What exists?" Different philosophers provide different answers to this question. One common approach is to divide the extant entities into groups called "categories." However, these lists of categories are also quite different from one another.
This highlights one of the problems of the philosophical approach—it relies on continued investigation of categories, and has no clear way to stop asking. Whereas, in theology and library science and artificial intelligence, one typically adopts a relatively stable foundation ontology. This reflects a larger cosmology, morals, aesthetic, stories; all of which can set foundational priorities. In theology this derives from a religion and its (relatively) stable doctrines.
Further examples of ontological questions include: