It is possible to prove that something of a certain sort does not exist.

It is often claimed that a good argument for atheism is impossible because, while it is at least possible to prove that something of a certain sort exists, it is impossible to prove that nothing of that sort exists. One reason to reject this claim is that the descriptions of some kinds of objects are self-contradictory. For example, we can prove that no circular square exists because such an object would have to be both circular and non-circular, which is impossible. Thus, one way to argue for t