that he is, in fact, doubting. He knows what he is thinking about, even if it is not true, and he knows that he is there thinking about it. From this basis, he builds his knowledge back up again. He finds that some of the ideas he has could not have originated from him alone, but only from God; he proves that God exists. He then demonstrates that God would not allow him to be systematically deceived about everything; in essence, he vindicates ordinary methods of science and reasoning, as fallible but not false.

List of rationalist philosophers: