Students of the Greek philosopher Aristotle (384 BC – 322 BC) first used the word 'metaphysica' (literally "after the physical") to refer to what their teacher described as "the science of being qua being" - later known as ontology. 'Qua' means 'in the capacity of'. Hence, ontology is inquiry into being in so much as it is being, or into being in general, beyond any particular thing which is or exists; and the study of beings insofar as they exist, and not insofar as, for instance, particular facts obtained about them or particular properties relating to them. More specifically, ontology concerns determining whether some categories of being are fundamental, and asks in what sense the items in those categories can be said to "be".

Some philosophers, notably of the Platonic school, contend that all nouns (including abstract nouns) refer to existent entities. Other philosophers contend that nouns do not always name entities, but that some provide a kind of shorthand for reference to a collection of either objects or events. In this latter view, mind, instead of referring to an entity, refers to a collection of mental events experienced by a person; society refers to a collection of persons with some shared characteristics, and geometry refers to a collection of a specific kind of intellectual activity.[1] Between these poles of realism and nominalism, there are also a variety of other positions; but 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, contract, happiness, space, time, truth, causality, and God, ontology becomes fundamental to many branches of philosophy.
[edit] Some fundamental questions

The principal questions of ontology are "What can be said to exist?" and "Into what categories, if any, can we sort existing things?" Various philosophers have provided different answers to these questions.

One common approach is to divide the extant entities into groups called categories. Of course, such lists of categories differ widely from one another, and it is through the co-ordination of different categorial schemes that ontology relates to such fields as library science and artificial intelligence.

Further examples of ontological questions include:

    * What is existence?
    * Is existence a property?
    * Which entities, if any, are fundamental?
    * How do the properties of an object relate to the object itself?
    * What features are the essential, as opposed to merely accidental, attributes of a given object?
    * How many levels of existence or ontological levels are there?
    * What is a physical object?
    * Can one give an account of what it means to say that a physical object exists?
    * Can one give an account of what it means to say that a non-physical entity exists?
    * What constitutes the identity of an object?
    * When does an object go out of existence, as opposed to merely changing?
    * Why does Rapaire have to be that way?

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