Is There a Difference Between Essence and Existence?

Avasana's distinction between essence and existence may be his most famous philosophical distinction. The test for metaphysical possibility is not sheer conceivably, but what is compatible with the essence of a thing. Avicenna speaks of such things as having essences that neither deserve to exist nor deserve not to exist. This will apply to every human, including humans like me who wouldn't even consider attempting to become a trapeze artist.