Quine Quote on Ontology: To Be Is To Be

Quote

"To be is to be the value of a variable." — W.V.O. Quine, From a Logical Point of View (1953), Essay 1: "On What There Is"

Historical Context

The question "what is there?" is as old as philosophy itself. Aristotle devoted an entire discipline — metaphysics — to the study of being qua being, and the history of ontology is a long argument about what kinds of entities populate reality: material objects, abstract forms, souls, numbers, possible worlds, properties, relations, events. When W.V.O. Quine published "On What There Is" in the Review of Metaphysics in 1948, later reprinted as the opening essay of From a Logical Point of View (1953), he brought to this ancient question an approach that was both radically new and deceptively simple. The tools were those of modern symbolic logic, particularly the theory of quantification developed by Gottlob Frege and Bertrand Russell. The result was a criterion of ontological commitment that would reshape the way analytic philosophers thought about existence.

Quine's essay is structured as a critique of two opposing errors in ontology, which he illustrates with two fictional interlocutors: McX and Wyman. McX is a naive realist who believes that whatever we can think or talk about must exist. If Pegasus does not exist, how can we meaningfully say "Pegasus does not exist"? To make sense of such a statement, McX concludes, there must be something — a mental image, a possible entity, a Platonic form — that the name "Pegasus" designates. Wyman, a more sophisticated philosopher, takes a different route: he distinguishes between being and subsistence. Pegasus does not have being (it does not exist in the actual world) but it has subsistence (it exists as a possible object of thought). Both McX and Wyman, Quine argued, fall victim to what he called "Plato's beard": the notion that non-being must in some sense be, since we can talk about it.

Quine's solution drew on Russell's theory of descriptions. Russell had shown that a sentence like "The present king of France is bald" does not require that there be a present king of France for the sentence to be meaningful. The sentence is logically analyzable as a quantified statement — "there exists exactly one entity that is presently king of France and that entity is bald" — which is false, not meaningless, if there is no present king of France. Similarly, Quine argued, "Pegasus does not exist" does not require that Pegasus be some kind of entity. It is simply a denial that anything answers to the name "Pegasus," a denial that can be expressed in the language of quantification without presupposing the existence of Pegasus.

The context in which Quine wrote was one of ferment in the philosophy of mathematics and logic. The logical empiricists, with whom Quine had studied during his European fellowship in 1932-1933, were deeply interested in the ontological commitments of scientific and mathematical theories. Carnap, in particular, had argued that ontological questions are either internal (settled within a linguistic framework) or external (genuine questions about what framework to adopt). Quine rejected this distinction, arguing that the question of what exists is a straightforward, if difficult, empirical question: what do our best theories quantify over? The dictum "to be is to be the value of a variable" was the concise expression of this position, and it became one of the most famous philosophical formulations of the twentieth century.

Meaning and Interpretation

The statement "to be is to be the value of a variable" is Quine's criterion of ontological commitment, compressed into a single, memorable sentence. Its meaning depends on understanding the logical notion of a bound variable. In first-order logic, a universally quantified statement like "for all x, if x is a dog then x is a mammal" contains a variable, x, that ranges over the entities in the domain of discourse. The variable is "bound" by the quantifier "for all," and the entities over which it ranges are the "values" of the variable. When we say "for all x," we are saying something about every entity that x could be — every value that the variable x could take. Similarly, an existentially quantified statement like "there exists an x such that x is a prime number greater than 2" asserts that at least one entity in the domain satisfies the condition, and the entities that could satisfy it are the values of the variable x.

Quine's insight was that this logical machinery provides a precise and objective criterion for what a theory is committed to. If a theory contains a statement like "there exists a number n such that n is prime," then the theory is quantifying over numbers — the variable n ranges over numbers, and numbers are values of that variable. The theory is, in Quine's phrase, "ontologically committed" to numbers. If the theory cannot be reformulated without quantifying over numbers — if numbers are indispensable to the theory's expressive power — then the theory genuinely commits its adherents to the existence of numbers. This is not a matter of philosophical intuition or metaphysical speculation; it is a matter of examining the logical structure of the theory and determining what it quantifies over.

The fuller formulation from the original essay reads: "To be assumed as an entity is, purely and simply, to be reckoned as the value of a variable." The shorter version, "to be is to be the value of a variable," which Quine used in subsequent writings and lectures, is a condensation that captures the core idea with characteristic directness. Both formulations express the same principle: existence is not a property that entities may or may not have, but a matter of what our theories quantify over. An entity exists, for Quine, if and only if our best theory of the world must quantify over it in order to be true.

This criterion has several striking implications. First, it makes ontology a scientific rather than a purely philosophical question. What exists is determined not by a priori reasoning but by the development of our best scientific theories. If physics needs to quantify over electrons, we are committed to electrons. If mathematics needs to quantify over sets, we are committed to sets. If our best theory of the world can dispense with a certain class of entities — if it can be reformulated without quantifying over them — then we are not committed to those entities, however natural it may feel to talk about them. This is the basis of the Quine-Putnam indispensability argument for mathematical realism: since mathematics is indispensable to our best scientific theories, and since we are committed to whatever our theories quantify over, we are committed to the existence of mathematical objects.

Second, the criterion implies that ontology is holistic. We cannot determine the ontological commitments of a single sentence in isolation, because the meaning of a sentence depends on its role within the broader theory. The question is not whether a particular sentence quantifies over a certain class of entities, but whether the theory as a whole can be reformulated without that quantification. This connects Quine's criterion of ontological commitment to his confirmation holism — the view that the web of belief faces the tribunal of experience as a whole, not sentence by sentence. Ontology, like epistemology, is a matter of the overall structure of our theory, not of individual claims.

Third, the criterion introduces a note of pragmatism into ontology. The question of what exists, on Quine's view, is ultimately the question of what ontology best serves the needs of science — which ontology is simplest, most explanatory, most consistent with the evidence. There is no "ultimate" ontology that is correct independently of our theories; there is only the ontology implicit in our best current theory, which may be revised as the theory evolves. This does not mean that ontology is arbitrary or conventional — the world constrains our theories, and some ontologies are clearly better than others — but it does mean that ontological questions are not settled by metaphysical intuition alone.

The Stanford Encyclopedia of Philosophy notes that Quine's criterion of ontological commitment remains the standard framework for ontological inquiry in analytic philosophy. Whether one accepts it or not — and many philosophers have challenged it, arguing that some entities exist without being quantified over, or that quantification over entities does not always carry ontological commitment — one cannot engage in serious ontological inquiry without engaging with Quine's dictum. The phrase "to be is to be the value of a variable" has become, in the words of one commentator, the most famous sentence in twentieth-century analytic philosophy, a formulation that transformed the ancient question of what there is into a precise and tractable problem at the intersection of logic, language, and science.