Existence

The condition of being real, as distinct from being merely thought of, described or defined.

Theme: Being and reality
Tradition: Cross-tradition
Term fixed: c. 1020

In plain terms

You can describe something completely and still not know whether there is one. A full specification of a unicorn tells you what a unicorn would be; it does not tell you that any exists. So existence is not one of the things in the description.

That sounds like a technicality and it decides several long arguments. If existence were a property, then a thing could be defined into being simply by including it - and there is a famous proof of God that works exactly that way, which is why the point matters.

What existence is instead is harder. On one account it is not a property of things at all but a fact about concepts: to say tigers exist is to say the concept tiger has instances. On another it is the most fundamental thing about a thing, and treating it as a logical footnote is how a whole tradition lost its subject.

As a philosopher would put it

Kant's objection in the Critique of Pure Reason is that being is not a real predicate: a hundred real thalers contain no more than a hundred possible ones, and adding existence to a concept adds nothing to it. Frege turns this into the standard modern treatment - existence is a second-order property, a property of concepts rather than objects, and tigers exist says that the concept tiger is instantiated. Russell's theory of descriptions extends it to the awkward cases: the present King of France does not exist becomes a claim about no object satisfying a description, so nothing has to be denied of an object that is not there.

Avicenna's framing runs the other way and is older. Essence considered in itself is neither existent nor non-existent; existence is something that arrives, which makes the existence of contingent things something requiring a cause and produces the argument from contingency.

Quine's slogan closes the modern debate: to be is to be the value of a bound variable. Ontology becomes a question about what our best theories quantify over.

Where you meet it

In 1846 Urbain Le Verrier calculated that irregularities in the orbit of Uranus required an unseen planet, worked out where it should be, and wrote to Berlin. Neptune was found the same night, within a degree of the prediction.

Thirteen years later he did it again. Mercury's perihelion was also shifting, the same mathematics gave the same kind of answer, and he announced a planet inside Mercury's orbit named Vulcan. Observatories reported it. Sightings were logged for fifty years.

Vulcan was never there. The anomaly was real, and in 1915 general relativity accounted for it with no extra planet. Two identical pieces of reasoning, both rigorous, both describing an object completely and specifying where to look - and one object existed while the other did not. Nothing internal to the description distinguished them. Only looking did.

What is actually disputed

Whether existence is a property at all.

The Frege-Russell-Quine line says no: it is a matter of instantiation, and the appearance that it is a feature things have is a trick of grammar. On that view the old question of why anything exists may not be well formed. Against this, the Avicennan and Thomist tradition holds that existence is the actuality of a thing rather than a fact about a concept, and that reducing it to quantification describes our talk while leaving the subject untouched.

A separate and unresolved argument concerns whether existence admits of kinds. Numbers, fictional characters, holes and shortages are all spoken of as existing or not; whether they exist in one sense, several senses, or only one of them exists at all, has no settled answer.

Commonly confused with

Being c. 475 BC Existence is that a particular thing is. Being is what it is for anything at all to be. Most European languages keep these apart; English does not.
physical presence A shortage, a debt and a right are all said to exist. Whether they exist in the same sense as a stone is exactly the open question.

Defined against

Nothingness What existence is contrasted with, and the contrast is older than either term

Philosophers

Avicenna Separates existence from essence, and makes it a question
Immanuel Kant Existence is not a real predicate, and the ontological argument falls
Thomas Aquinas Existence as actuality rather than as a logical feature
Willard Van Orman Quine To be is to be the value of a bound variable
Bertrand Russell Descriptions, and how to deny existence without denying it of something

Works

The Book of Healing Where essence and existence come apart
Critique of Pure Reason The argument that existence adds nothing
Summa Theologiae Existence as act, and the contingency argument
Principia Mathematica The logical machinery the modern account runs on

Schools

Avicennism Where the distinction is drawn
Thomism Where it becomes an argument about God
Vienna Circle Where existence questions are reduced to logic
Nominalism Where abstract existents are refused

Related concepts

Being c. 475 BC · Essence c. 330 BC · Contingency c. 1020 · Necessity c. 330 BC · Nothingness c. 475 BC

Avicenna made existence a separate question from essence around 1020, which is the point at which it becomes a subject rather than an assumption.