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Originally Latin ontologia (1606, Ogdoas Scholastica, by Jacob Lorhard (Lorhardus)), from Ancient Greek ὤν (ṓn, on), present participle of εἰμί (eimí, being, existing, essence) + λόγος (lógos, account).

First known English use 1663: Archelogia philosophica nova; or, New principles of Philosophy. Containing Philosophy in general, Metaphysicks or Ontology, Dynamilogy or a Discourse of Power, Religio Philosophi or Natural Theology, Physicks or Natural philosophy, by Gideon Harvey (1636/7-1702), London, Thomson, 1663.

Popularized as a philosophical term by German philosopher Christian Wolff (1679–1754).



ontology (plural ontologies)

  1. (uncountable, philosophy) The branch of metaphysics that addresses the nature or essential characteristics of being and of things that exist; the study of being qua being.
    • 2014 April 12, Michael Inwood, “Martin Heidegger: the philosopher who fell for Hitler [print version: Hitler's philosopher]”, in The Daily Telegraph (Review)[1], London, page R10:
      [Martin] Heidegger's concern [] was with ontology, the nature of beings, above all humans. The central question for him was "What is being? What is it for something to be?" He tackled this question not by way of the sciences, but by way of an examination of our prescientific daily life. We are, he argued, not cut off from the world by our mental processes: we are "in the world", in direct contact with our surroundings.
  2. (countable, philosophy) The theory of a particular philosopher or school of thought concerning the fundamental types of entity in the universe.
    • 2000, C. D. C. Reeve, Substantial Knowledge: Aristotle's Metaphysics, Hackett Publishing, p. 97:
      The answer to the controversial question of whether Aristotle's ontology includes non-substantial particulars, then, is that it does.
  3. (logic) A logical system involving theory of classes, developed by Stanislaw Lesniewski (1886-1939).
  4. (computer science, information science) A structure of concepts or entities within a domain, organized by relationships; a system model.

Usage notes[edit]

In the field of philosophy there is some variation in how the term ontology is used. Ontology is a much more recent term than metaphysics and takes its root meaning explicitly from the Greek term for being. Ontology can be used loosely as a rough equivalent to metaphysics or more precisely to denote that subset of the domain of metaphysics which is focused rigorously on the study of being as being.


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  • ontology in An American Dictionary of the English Language, by Noah Webster, 1828.
  • ontology in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.
  • ontology” in Dictionary.com Unabridged, Dictionary.com, LLC, 1995–present.
  • ontology” in Microsoft's Encarta World English Dictionary, North American Edition (2007)
  • ontology” in the Compact Oxford English Dictionary (Oxford University Press, 2007)
  • "ontology" by F.P. Siegfried, in The Catholic Encyclopedia (Robert Appleton Company, New York, 1911)
  • Oxford English Dictionary, second edition (1989)
  • Random House Webster's Unabridged Electronic Dictionary (1987-1996)
  • Dictionary of Philosophy, Dagobert D. Runes (editor), Philosophical Library (1962); see: "Ontology" by James K. Feibleman, page 219
  • "Ontology" by Tom Gruber to appear in the Encyclopedia of Database Systems, Ling Liu and M. Tamer Özsu (editors), Springer-Verlag (2008)