Existence raises deep and important problems in metaphysics, philosophy of language, and philosophical logic. Many of the issues can be organized around the following two questions: Is existence a property of individuals? and Assuming that existence is a property of individuals, are there individuals that lack it?
Bertrand Russell expressed one aspect of the problem this way: If it’s false that the present King of France is bald, then why doesn’t this fact imply that it’s true the present King of France is not bald?
Kant argues that the use of words (or “predicates”) alone does not necessarily imply the existence of their referents. We can only assume the existence of entities named by our words; we cannot prove “existence” by means of the use of language alone.