ONTOLOGY (adapted from a modern Latin form ontologia used by Jean le Clerc 1692; Gr. ὤν, ὄντος, pres. part, of εἷναι to be, and λόγος, science), the name given to that branch of philosophy which deals specially with the nature of being (οὐσία) i.e. reality in the abstract. The idea, denoted in modern philosophy by the term “ontology” in contrast to the broader “metaphysics” and the correlative “epistemology,” goes back to such phrases as ὄντως ὄντα, which Plato uses to describe the absolute reality of ideas; Plato, however, uses the term “dialectic” for this particular branch of metaphysics. Aristotle, likewise, holding that the separate sciences have each their own subject matter, postulates a prior science of existence in general which he describes as “first philosophy.” So far, therefore, the science of being is distinguished not from that of knowing but from that of the special forms of being: as to the possibility of objective reality there is no question. A new distinction arises in the philosophy of Wolff who first made “ontology” a technical term. Theoretical philosophy (metaphysics) is by him divided into that which deals with being in general whether objective or subjective, as contrasted with the particular entities, the soul, the world and God. The former is ontology. This intermediate stage in the evolution of the science of being gave place to the modern view that the first duty of the philosopher is to consider knowledge itself (see Epistemology), and that only in the light of conclusion as to this primary problem is it possible to consider the nature of being. The evolution of metaphysics has thus relegated ontology to a secondary place. On the other hand it remains true that the science of knowing is inseparable from, and in a sense identical with that of being. Epistemological conclusions cannot be expressed ultimately without the aid of ontological terms.
For the wider relations of ontology, see further Philosophy.