We explain what ontology is, its origin and major figures. In addition, we explore its relationship with metaphysics, its objectives and problems.

Ontology is part of metaphysics and studies being in general.

What is ontology?

Ontology is a philosophical discipline, a branch of metaphysics, whose object of study is being (viewed in a general sense). Ontological philosophers point out ontology's primary character when compared to other branches of metaphysics and even metaphysics itself.

Various authors in the history of philosophy have made ontology their primary philosophical concern, including Aristotle and St. Thomas Aquinas. However, the first to popularize the term was Christian Wolff (1679-1754), who defined it as the science of being in general (scientia entis in genere, quatenus ens ens). He established being as the general component of entities, and posed the difficulty of defining both ontology and being.

Also known as "general metaphysics", ontology addresses questions like the meaning of being, the ways to classify it and various ontological issues, such as universality, necessity and possibility.


  • Ontology is part of metaphysics and studies the nature of being as such. It is considered a science of essences.

  • It differs from metaphysics, which studies the principles and fundamental causes of philosophical thought and being as supreme entity.

  • Ontological issues are concerned with what being is, and with the relationship between soul and matter, among other questions.

Origin of ontology

Etymology: The word "ontology" has its origin in Ancient Greek tou ontos logos (τοῦ οντος and λόγος), whose literal translation is "study of the entity" or "study of what exists". Its field of study is being as the common characteristic to all that exists.

Ontology according to Aristotle

Although it was Wolff who popularized the term, Aristotle in his Metaphysics already spoke of ontology as first philosophy. Its object of study as a form of metaphysics was "being as being" (ens qua ens). While in this sense the object of study was the entity, what made the entity an entity was its essence, its "what is": being.

The term Aristotle used to refer to essence is ousía (ουσία). Ousia is a substance that subsists by itself. It can be pointed at by means of deictics "this" or "that". In the sense of "being", ousia is what is being here and now. Thus the term ousia came to mean the "essence of the concrete individual entity", which is indefinable but can be studied by abstracting the form from the entity.

Aristotle asserted that form is the being of each thing and its primary reality, in this way unifying "being" with "essence".

Ontology according to other thinkers

  • Christian Wolff. Based on the works of Aristotle and Leibniz, Wolff took up the term "ontology" to refer to first philosophy or general metaphysics.
  • Immanuel Kant. He defined metaphysics as an ontology concerned with synthetic a priori knowledge of things (what can be acquired independently of experience). He turned ontology towards the study of the concepts of understanding that made the knowledge of things possible.
  • Edmund Husserl. He used the word "ontology" to speak of "regional ontologies", which are descriptions of regional essences or “regions of being”, such as society, nature or morality.
  • Martin Heidegger. He took up ontology to support metaphysics, regarding the former as the science that concerns itself with the being of man or dasein ("being-there"): a “being-in-the-world”, a “being-as-such”.

20th-century ontology

Contemporary philosophy owes its conception of ontology to 20th-century philosophy. Authors like Husserl, Heidegger, Nicolai Hartmann, J. Feibleman, Lésniewski, and Quine approached the idea of ontology differently. Below are some of these approaches:

  • Ontology according to Edmund Husserl. Husserl presented ontology as a science of essences. Accordingly, he distinguished between two forms of ontology:
    • Formal ontology. It deals with formal essences. By integrating material ontology, it encompasses all possible ontologies. It is the foundation of all sciences.
    • Object ontology. It deals with material essences, that is, it is concerned with regional ontologies. It lies within formal ontology and is the foundation of the factual sciences.
  • Ontology according to Martin Heidegger. Heidegger coined the term fundamental ontology. It is a metaphysics of existence which seeks out to discover the meaning of being. It is called fundamental because it aims to reveal what constitutes the foundation of existence, i.e. its finitude. Thus by devoting itself to finitude as the basis of existence, the task of fundamental ontology is to investigate being as being-as-such and not as a mere formal entity.
  • Ontology according to Nicolai Hartmann. For Hartmann, ontology’s task is not to solve all problems but to recognize what is metaphysically insoluble (i.e. what cannot be solved by metaphysics).
  • Ontology according to Jamés Feibleman, Stanislaw Lésniewski and W. V. O. Quine. These authors thought about ontology outside the traditional schools of philosophy, such as rationalism, phenomenology or existentialism. Feibleman presented a "finite" form of ontology that should mediate between the metaphysical and the positivist attitude. Lésniewski introduced into his ontology his theory of calculus of names and sets. Quine, for his part, divided semantics into the theory of reference and the theory of meaning, assigning ontology to the former, thus making it an "ontology of" a theory, not a general ontology.

Ontological problems

Ontological problems are discussions arising when thinking about the existence of different entities. As Quine suggests, the quintessential ontological problem lies in the question "What is there?" whose answer, or at least that one formulated by Quine, is “everything”, that is to say, “there is what there is”.

Beyond the issue raised by Quine, ontological problems are those related to the question of being or the meaning of what is.

Among the most commonly acknowledged ontological problems are:

  • The problem of universals and particulars, which asks what is shared by sensible particulars.
  • The problem of abstract entities, which asks about concrete and abstract entities.
  • The problem of identity and persistence, which asks how an object can remain the same over time.
  • The problem of mind-body dualism, which asks about the relationship between mind or soul and matter.
  • The problem of the hole argument, which asks about the essence of holes and the possibility of defining them through language.

Ontology and metaphysics

The confusion between the two terms comes from the fact that the philosophers who used the word "ontology" did so to refer to its primary nature when compared to any other form of metaphysics. Most of them called ontology "general metaphysics", as opposed to "special metaphysics".

Ontology as general metaphysics was the first rational science par excellence. Its task was to determine the study of all questions and issues related to the "highest" genera of concrete entities (beyond accidental or temporal traits).

At its core, ontology concerned itself with the formalities regarding the general classification of entities and the distinctions and concepts that all entities have in common, as can be seen in the scholastic works carried out by Catholic Church scholars, on the one hand, and in Kantian philosophy with a priori concepts, on the other.

Broadly speaking, given its closeness to metaphysics, there are two ways of understanding ontology:

  • Ontology as a science of being-in-itself, on which all other entities depend. This is the truly metaphysical sense of ontology as the science of existence.
  • Ontology as a science that determines what entities have in common and what being consists of. This is the sense of ontology as the science of essences or pure ontology.

Notable ontologists

Whether knowing or not, many philosophers and thinkers devoted themselves to ontology or the science of being.

Among them are:

  • Aristotle (384-322 BC). The great Ancient Greek thinker, he is credited as the first to systematize the problem of being.
  • René Descartes (1596-1650). He revolutionized modern metaphysics, ontology and philosophy.
  • Parmenides (530-460 BC). He laid the foundation for the reflection on being.
  • Heraclitus (540-480 BC). A contemporary of Parmenides, he introduced temporality and becoming to the question of being.
  • Thomas Aquinas (1225-1274). He contributed by taking up Aristotelian ontology and introducing it into Christian theology.
  • Avicenna (980-1037). Like Thomas Aquinas, he took up the work of Aristotle and introduced it to Islamic theology.
  • Gottfried Leibniz (1646-1716). He explained the ontological universe through monads and reflected on contingency and necessity.
  • Baruch Spinoza (1632-1677). Through his Ethics, he analyzed divine ontology, making metaphysics and theology coincide.
  • Immanuel Kant (1724-1804). He is credited with unifying rationalist thought and empiricism, giving way to a critical analysis of reason.
  • Edmund Husserl (1859-1938). The founder of phenomenology, he built upon the concepts of being and becoming. He thought of ontology as a science of essences.
  • Martin Heidegger (1889-1976). A student of Husserl and his critical successor, he wrote the most important book of the 20th century, Being and Time.
  • Nicolai Hartmann (1882-1950). He thought of ontology as the science that must know what is metaphysically insoluble.
  • Gilles Deleuze (1925-1995). He related ontology with politics and aesthetics.
  • Rudolf Carnap (1891-1970). He reflected on various ontological problems, such as the problem of abstract entities.
  • Jean-Paul Sartre (1905-1980). The founder of existentialism, he developed a phenomenological ontology through his work Being and Nothingness.
  • V. O. Quine (1908-2000). He elaborated an ontology of theory based on the objects that the theory postulates.

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ESPÍNOLA, Juan Pablo Segundo. "Ontology".
Encyclopedia of Humanities. 18 January, 2024, https://humanidades.com/en/ontology/.

About the author

Author: Juan Pablo Segundo Espínola

Bachelor of Arts in philosophy (University of Buenos Aires)

Translated by: Marilina Gary

Degree in English Language Teaching (Juan XXIII Institute of Higher Education, Bahía Blanca, Argentina).

Updated on: 18 January, 2024
Posted on: 28 September, 2023

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