Gassendi and Kant on Existence

In rejecting Descartes's ontological proof for the existence of God, Gassendi maintained that existence is not a property and Kant said that it is not a "real predicate." It is commonly supposed that both are making the same claim. Some have even thought that they advance essentially the same argument for that same claim. I believe none of this is correct. Gassendi and Kant offer different arguments. And they are arguing for different conclusions. These differences stem from a more fundamental one: they mean different things by existence.