What Is Ontology as a Philosophical Doctrine

Ontology, in its broadest sense, is the philosophical study of being: the systematic inquiry into what exists, what kinds of things exist, and what it means for something to exist at all. As a doctrine, it is the claim that these questions admit of rigorous, rational answers — that we can, by argument and analysis, determine the inventory of reality. The name combines the Greek ontos ("of being") and logos ("study"), and the enterprise is often summarized as asking: what is the furniture of the universe?

Ontology is sometimes presented as a doctrine in a narrower sense: the commitment to a particular inventory of what exists. A "substance ontology" holds that the world is ultimately composed of substances; a "process ontology" holds that it is composed of events and processes; a "nominalist ontology" holds that only particulars exist, denying universals. In this sense, to have an ontology is to have a theory of what there is. The philosophical discipline of ontology is the arena in which such theories are constructed, compared, and criticized.

Historical Background

Ontology begins with Aristotle. In the Categories, he proposed that everything that exists falls into one of ten categories — substance, quantity, quality, relation, and so on — and argued that substance is primary, since qualities, quantities, and relations exist only as attributes of substances. In the Metaphysics, he asked what being is and answered that it is said in many ways, all related to the primary sense of substance. Aristotle's substance ontology dominated Western philosophy for nearly two millennia, shaping the medieval debates about universals (do general properties exist?) and about essence and existence (is existence part of what a thing is?).

The modern period brought new questions. Descartes's dualism of mind and substance, Spinoza's single substance, Leibniz's monads — each was an ontology, a claim about the ultimate inventory of reality. Kant attempted to restrict ontology to the conditions of possible experience, arguing that we cannot know what exists independently of the forms of our cognition. The twentieth century saw ontology revive in two very different keys. In the analytic tradition, W. V. O. Quine made ontology respectable again by tying ontological commitment to the existential quantifiers of our best scientific theories: "to be is to be the value of a variable." In the continental tradition, Heidegger transformed ontology into "fundamental ontology": not a catalogue of entities but an inquiry into the meaning of Being itself, conducted through the analysis of human existence (Dasein).

Key Arguments

The Argument for Categories

Aristotle's argument for a substance ontology rests on the grammar of predication and change. When we say that the rose is red, we attribute a quality to a substance; when the rose withers, it is the same substance that changes its qualities. Without substances, there would be nothing that persists through change and nothing that supports attributes. The nominalist reply denies that we need to posit universals or abstract qualities: "red" is just a word applied to many particulars, and "substance" is just a grammatical subject. The debate between realist and nominalist ontologies has run for over two thousand years and remains unresolved.

The Argument from Scientific Commitment

Quine's criterion of ontological commitment made the question of what exists a matter of what our best theories say exists. If our best physics quantifies over electrons and fields, then electrons and fields exist; if our best mathematics quantifies over numbers, then numbers exist. This "naturalistic" approach to ontology has two consequences: it makes ontology continuous with science, and it forces us to take seriously the abstract objects that mathematics and logic seem to require. The argument for their existence is the indispensability argument: our best theories quantify over them, and we should believe what our best theories say. The nominalist replies that we can paraphrase away the apparent commitment — or that the argument proves too much.

The Argument from Being and Time

Heidegger's argument for a fundamental ontology begins with a diagnosis: the tradition has forgotten the question of Being, treating Being as a thing, a property, or a mere word. His remedy is to analyze the being for whom Being is an issue — Dasein, the human way of being — and to show that the meaning of Being is inseparable from temporality. The argument's conclusion is radical: ontology is not a science of the most general kinds of entity but the most concrete inquiry of all, because it is the inquiry into what it is to be the kind of being that asks about being. Whether this is a continuation or a repudiation of classical ontology remains a central interpretive question.

Contemporary Relevance

Ontology today is a vigorous and technically sophisticated field. Analytic metaphysicians debate the existence of abstract objects, possible worlds, and mereological sums with arguments of great precision, and ontology is increasingly connected to the sciences — to physics (what does fundamental physics tell us exists?), to biology (are species real?), to the cognitive sciences (what ontology do agents employ?), and to computer science, where "ontologies" are formal specifications of the concepts and relations in a domain. The philosophical debates have practical stakes: the question of whether mental states, moral properties, or mathematical objects are real shapes how we understand the authority of science, ethics, and mathematics alike.

Sources

• Internet Encyclopedia of Philosophy, "Ontology"
• Stanford Encyclopedia of Philosophy, "Aristotle's Metaphysics"
• Stanford Encyclopedia of Philosophy, "Martin Heidegger"
• Stanford Encyclopedia of Philosophy, "Abstract Objects"

Related Topics

• Ontology as a topic — the hub for the study of what exists
• Metaphysics — the wider discipline to which ontology belongs
• Being — the object of ontological inquiry
• Existence — the mode of being that ontology investigates
• Reality — the everyday name for what ontology studies