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Learned borrowing from New Latin ontologia (1606, Ogdoas Scholastica, by Jacob Lorhard (Lorhardus)), from Ancient Greek ὤν, ὄντος (ṓn, óntos, being), 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 (1636–1702), London, Thomson, 1663.

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


  • IPA(key): /ɒnˈtɒləd͡ʒi/
  • (file)
  • Rhymes: -ɒlədʒi


ontology (countable and uncountable, plural ontologies)

Examples (Concepts in ontologies of various subject or world views)

Atoms, molecules, ions and electrons occur in the ontology of chemistry.
Witches, magic, and unlucky numbers occur in the ontology of superstitions
Theorems, constants, and variables occur in the ontologies of axiomatic structures

  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. (uncountable, philosophy) In a subject view, or a world view, the set of conceptual or material things or classes of things that are recognised as existing, or are assumed to exist in context, and their interrelations; in a body of theory, the ontology comprises the domain of discourse, the things that are defined as existing, together with whatever emerges from their mutual implications.
    • 2017, Daniel C. Dennett, From Bacteria to Bach and Back, →ISBN:
      Do you believe in ghosts? Then ghosts are in your ontology, along with tables and chairs and songs and vacations, and snow, and all the rest. It has proved more than convenient to extend the term "ontology" beyond this primary meaning and use it for the set of "things" that an animal can recognize and behave appropriately with regard to (whether or not animals can properly be said to have beliefs) and — more recently — the set of "things" a computer program has to be able to deal with to do its job (whether or not it can properly be said to have beliefs). Vacations are not in the ontology of a polar bear, but snow is, and so are seals. Snow is probably not in the ontology of a manatee, but outboard-motor propellers may well be, along with seaweed and fish and other manatees. The GPS system in your car handles one-way streets, left and right turns, speed limits, and the current velocity of your car (if it isn't zero, it may not let you put in a new target address), but its ontology also includes a number of satellites, as well as signals to and from those satellites, which it doesn't bother you with, but needs if it is to do its job.
  3. (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, page 97:
      The answer to the controversial question of whether Aristotle's ontology includes non-substantial particulars, then, is that it does.
  4. (logic) A logical system involving theory of classes, developed by Stanislaw Lesniewski (1886-1939).
  5. (countable, 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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