QuestionsDoes God exist?Existence is not a predicate
Does God exist?AgnosticismOntological

Existence is not a predicate

Immanuel Kant 1724 · 1804Set the limits of reason; act from duty.
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What it claims

The ontological proof fails: God's existence cannot be deduced from his concept alone.

Why

Existing adds nothing to the concept of a thing: a hundred real thalers contain no more than a hundred imagined ones.

In short

"Existence is not a predicate" is an argument by Immanuel Kant (Critique of Pure Reason, A598/B626) on the question "Does God exist?" (answer: agnosticism). Its claim: The ontological proof fails: God's existence cannot be deduced from his concept alone. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 3 premises. AskPhilosophy presents 2 objections, 2 of them with a documented reply, and the original text behind each premise, checked word for word.

Critique of Pure Reason, A598/B626
Valid

The ontological proof (Anselm, Descartes) derives God's existence from the mere idea of a perfect being. Kant shows why, in his view, it fails.

P1"Existing" adds nothing to the concept of a thing: a hundred real thalers contain nothing more than a hundred imagined ones.
P2If the ontological proof succeeded, existence would have to be a property contained in the concept of God, like omnipotence.
P3Denying that God exists removes the subject with all its properties: there is no contradiction in that.
Therefore the ontological proof fails: God's existence cannot be deduced from his concept alone.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
P1 and P2 are enough to make the argument valid; P3 reinforces the point but is not essential. The heart of the debate is P1: is existence (or necessary existence) really without content?
Analogy. Draw the blueprint of a perfect house and add the note "exists". The blueprint is no more complete, and no house appears. For Kant, "exists" is not a feature of the blueprint: it is the fact that a real thing corresponds to it.

Objections

2

Each objection is a conversation: click to see who replies and where the debate stands.

Descartes (anticipated defence) 1641 · attacks premise 2

The proof is not about ordinary existence but about necessary existence, which only the idea of God contains. It is not a predicate like any other.

Kant replies
Kant
Even necessary existence adds nothing to the subject: if I deny that God is, I remove the subject with all its predicates, necessity included, without any contradiction.
Where the debate stands (our summary)Kant replies that removing God also removes his necessity, without contradiction. The proof's defenders (Malcolm, then Plantinga) move the debate to necessary existence, then to the modal version, where everything depends on the question "is such a being possible?" (see the arguments of Anselm and Plantinga).
Alvin Plantinga 1974 · attacks premise 2

A modal version of the proof need not treat existence as a predicate: if a maximally great being is possible, it exists in every possible world. The debate shifts to the premise "it is possible".

Kant replies
summary: their text is not yet in our corpus
No reply possible: objection raised in 1974, after the author's death (1804).
G
Graham Oppy, Joshua Rasmussen and Joseph Schmid 2024
These authors do not defend Kant's thesis: they even judge that general objections of this kind rest on highly contested assumptions. They grant that the modal version avoids treating existence as an ordinary property, but it rests on the premise "a maximally great being is possible". One can write the reverse premise ("it is possible that no such being exists"); without an independent reason to prefer the first, the argument cannot convince. The rest of the debate is in the modal argument.
see the argument
Where the debate stands (our summary)According to its defenders, the modal version escapes the objection "existence is not a predicate"; its present-day critics attack it from another side, moving the debate to the possibility of a maximally great being. Defenders and critics disagree there, with no universally accepted independent reason to settle it.
In the same family · Ontological
The ontological proofRené Descartes
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God is not a hundred thalers: Hegel defends the ontological proof against KantGeorg Wilhelm Friedrich Hegel
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That than which nothing greater can be conceived existsAnselme de Cantorbéry · 1078 · debate over 3 levels
Does God exist?Theism 5
If it is possible, it exists: the modal ontological argumentAlvin Plantinga · 1974 · debate over 3 levels
Does God exist?Theism 4