Full Idea
Kant's famous critique of the Ontological Argument that existence is not a predicate leaves one perplexed as to what it might be, but modern logic says that existence is a quantifier, not a predicate.
Gist of Idea
Modern logic says (with Kant) that existence is not a predicate, because it has been reclassified as a quantifier
Source
comment on Immanuel Kant (Critique of Pure Reason [1781]) by José A. Benardete - Metaphysics: the logical approach Ch.10
Book Reference
Benardete,José A.: 'Metaphysics: The Logical Approach' [OUP 1989], p.63
A Reaction
See McGinn's criticism of this in Idea 6062.
Related Idea
Idea 6062 Existence can't be analysed as instantiating a property, as instantiation requires existence [McGinn]