The Joker cannot doubt Batman's existence when with him, but can doubt Bruce Wayne's existence, yet Bruce Wayne is identical to Batman

The argument is fallacious. It relies on conceivability based in ignorance. Descartes has not included anything in the argument to ward off the possibility that he, as a thinking thing, is in fact a complex material system. He has merely relied on the fact that he can doubt the existence of matter to conclude that matter is distinct from mind. This argument is clearly inconclusive. From the fact that the Joker cannot, at a certain moment, doubt the existence of Batman (because he is with him), b