Ontology is a philosophical discipline that examines concepts related to being, including existence, reality, and the fundamental categories of being and their interrelationships. The term derives from the Greek words for 'being' and 'logical discourse'. First seen in the work of Jacob Lorhard and Rudolf Göckel in the early 17th century, the term was widely used by philosophers based on its Latin roots, with Leibniz being the notable user amongst the great philosophers of the era.

Ontology studies questions like "What can be said to exist?" "What is a thing?" "What are the meanings of being?" and "What are the various modes of being of entities?". Various philosophers offer different answers to these questions, often categorizing subjects and predicates into groups called categories, which differ from one philosopher to another. Aristotle's categories, for instance, include how a being may be addressed, its 'whatness', 'howness', quantitativeness, and its relatedness to other beings.

Further ontological inquiries delve into the nature of existence, the properties of an object, the levels of existence, the nature of physical and non-physical entities, the identity of an object, and the existence of beings beyond the subject/object split of modern philosophy. Central ontological dichotomies encompass universals and particulars, substance and accident, abstract and concrete objects, essence and existence, determinism and indeterminism, monism and dualism, and idealism and materialism.

Ontologies can be classified in various ways based on their abstraction degree and application field. They include Upper ontology (meta-ontology), Domain ontology (specific to a particular area), Interface ontology (relevant to the intersection of two disciplines), and Process ontology (pertinent to business or engineering processes).

Historically, ontology has been part of various philosophical traditions. In Hindu philosophy, the Samkhya school discussed ontology as early as the first millennium BCE, proposing the concept of 'guṇa', which describes the three properties present in all existing things. The Greek philosopher Parmenides was among the first to provide an ontological characterization of existence, positing that nothing comes from nothing, existence is eternal, uniform, immutable, and there is neither void nor vacuum. He argued that the change we perceive in our daily experience is illusory, and everything is part of a single entity. This idea hints at a modern concept of a grand unification theory that describes all of existence in terms of an interrelated subatomic reality.

Ontological pluralism, the antithesis of Parmenides’ Eleatic monism, embodies the concept of becoming and elemental ontic plurality. This was introduced in the Hellenic world by Anaxagoras and Leucippus, with differing theories of the substance and structure of reality. Leucippus' indeterminist atomism, later adapted deterministically by Democritus and reasserted as indeterminist by Epicurus, proposed a reality constructed of atoms in intrinsic motion, subject to chance.

Plato, in contrast, emphasized the division between true reality and illusion, contending that the real are eternal and unchanging Forms or Ideas. For Plato, all entities, whether tangible bodies or insensible Forms, referred to real entities. He argued for the existence of Forms, even those of Non-Being and Negation, opposing Parmenides.

Aristotle, in his "Categories," identified ten potential things that could be the subject or predicate of a proposition and offered four different ontological dimensions, including categories of a being, its truth or falsity, its existence in and of itself or by accident, and its potency, movement, or finished presence.

Avicenna's interpretation of Greek Aristotelian and Platonist ontological doctrines suggested that being could be necessary, contingent, or impossible. Necessary being is inescapable, as its non-existence would contradict. Contingent being is neither necessary nor impossible and relies on external cause to move from potential to actual existence.

The concept of ‘ontological formations’ refers to the predominant ways of living, determined by temporal, spatial, corporeal, epistemological and performative relations. These formations are understood to be layered and intersecting. They offer a framework for designing cities and communities that can function creatively across different ontological formations.

Descartes argued for the epistemological certainty of the self and the existence of God using the ontological argument. The Cartesian understanding of the self and the other, however, faced criticism in the 20th century from sociological theorists like George Herbert Mead and Erving Goffman.

There has been a shift in questioning the meaning of being from subjectivism, objectivism, and relativism to the action of bodies in an environment. This view, prominent in the 20th century, was influenced by scientific research into animal behavior. The relationship between bodies and their environments became critical, and the definition of being became elusive. Heidegger differentiated human existence from the existence of things in the world and proposed that our way of being is shaped by a fundamental ontological questioning.

The philosophical discussion on ontology - the branch of metaphysics dealing with the nature of being - is presented in multiple contexts. One such context relates to language, where it is argued that the question of "what is?" might partly be about how we use language rather than about facts. The discussion suggests that different cultures or societies might use language differently to refer to the same object. This understanding is used to interpret different concepts of "the existence of something," which may vary across languages or cultures.

The essay also discusses ontology in relation to human geography, distinguishing between small “o” ontology, which oversimplifies the functions of being a part of a group, and big “O” ontology, which logically describes essential characteristics and universal traits. It further emphasizes the importance of symbolic agreements among members within this context.

The distinction between ‘reality’ and ‘actuality’ is another topic, with an ‘actual entity’ considered to have fundamental ontological priority over a ‘real entity,’ which may derive its reality from its relation to some actual entity or entities. Here, the emphasis is on an actual entity being completely determinate and unique, thus earning its philosophical status of fundamental ontological priority.

The essay continues with a discussion of microcosmic ontology, focusing on the debate around the real existence of atoms and subatomic particles, given their microscopic size. This discourse also raises questions about the physical properties of these particles, such as their precise position and momentum, and how the quantum mechanical wave function refers to them.

The ontological argument for the existence of God, as proposed by Anselm of Canterbury and later by René Descartes and Gottfried Leibniz, is also covered. Here, the argument posits that if the greatest possible being exists in the mind, it must also exist in reality, asserting the existence of God.

Finally, the document touches upon Jaakko Hintikka's interpretation of the notion of existence, paraphrasing it as "one can find", implicitly referring to some world or universe of discourse. This view represents another approach to understanding ontology and the concept of existence.

Prominent ontologists

Anselm of Canterbury

Thomas Aquinas



David Malet Armstrong

Alain Badiou

Gustav Bergmann

Roy Bhaskar

Bernard Bolzano

Franz Brentano

Martin Buber

Mario Bunge

Rudolf Carnap

Ernst Cassirer

Gilles Deleuze

Daniel Dennett

Jacques Derrida

René Descartes

Fyodor Dostoevsky

Maurizio Ferraris

Michel Foucault

Richard Foreman

Hans-Georg Gadamer


Étienne Gilson

Nicolai Hartmann

Georg Wilhelm Friedrich Hegel

Martin Heidegger

Heraclitus of Ephesus

Jaakko Hintikka

Edmund Husserl

Roman Ingarden

Immanuel Kant

Leszek Kołakowski

Julia Kristeva

Susanne Langer

Louis Lavelle

Gottfried Leibniz

Douglas Lenat

Stanisław Leśniewski


David Kellogg Lewis

Emmanuel Levinas

John Locke

E.J. Lowe


Alexius Meinong


Friedrich Nietzsche

Keiji Nishitani


Charles Sanders Peirce



Karl Popper

Proclus Lycaeus

W.V.O. Quine


Bertrand Russell

Gilbert Ryle

Mulla Sadra

Jean-Paul Sartre

Jonathan Schaffer

Arthur Schopenhauer

Duns Scotus

John Searle

Adi Shankaracharya

Theodore Sider

Peter Simons

Barry Smith

Baruch Spinoza

Shahab al-Din Suhrawardi

Peter van Inwagen

Achille Varzi

Gianni Vattimo

Swami Vivekananda

Alfred North Whitehead

William of Ockham

Ludwig Wittgenstein

Edward N. Zalta

Dean Zimmerman

Slavoj Žižek

Nothing comes from nothing