In PHI 220 today, we considered Descartes' ontological argument for God's existence. One objection to that argument, which we see in Caterus's remarks, is that by Descartes' argument, one could prove that anything exists. For instance, we could prove a priori--not through empirical research--that lions exist just by stipulating that we are to consider the idea existing lion. By the same token, I could prove that mermaids exist by asking you to consider the idea of an existing mermaid. It's part of the idea of an existing mermaid that such a thing exist. Therefore, mermaids exist.
Note something about this argument: the idea, existing lion, is one that Caterus made up. The idea, existing mermaid, is one that I made up. And as I noted at the end of class today, Descartes seems concerned to convince us that we did not make up the idea of God:
Is this the beginning of a response to Caterus's objection? Does it matter that our idea of God is not one that we invented (assuming, in fact, that we did not invent it)?