Ontology — The branch of philosophy that studies being as being (from the Greek tò ón, “that which is,” and lógos, “discourse” or “study”): it investigates what exists, what the modes of existence are, and what the fundamental categories of the real are. Unlike the particular sciences, which deal with determinate regions of what exists (bodies, numbers, living things), ontology asks after the being of everything that is, prior to any regional division. Although the term itself is modern — already recorded in Jacob Lorhard (Ogdoas Scholastica, 1606) and spread by Goclenius’s Lexicon philosophicum (1613) — the inquiry it names goes back to Greek philosophy. Parmenides holds that “being is and non-being is not,” and Aristotle, in the Metaphysics, defines a science that studies “being qua being,” ordering the real through the categories (substance, quantity, quality, relation, and so on). In the 18th century, Christian Wolff fixed both the name and the program of the discipline in his Philosophia prima sive Ontologia (1730), raising it to the rank of first philosophy. In the 20th century, Heidegger reopened the question of being (Seinsfrage), charging the tradition with having confused being with beings, and proposed, in Being and Time, a fundamental ontology starting from the analysis of human existence. Ontology is thus distinguished from metaphysics (with which it partly overlaps) and is closely related to special metaphysics and to the theory of categories, which classifies the basic ways in which something can be said to exist.
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