I suppose one might ask the question "Does there exist anything that isn't part of the world of appearances (which may or may not be hallucinatory)?"David Quinn wrote:Empirical phenomena are part of the world of appearances, which may or may not be hallucinatory, in which no certainty can be found. Pinning one's hopes on the existence of a particular empirical phenomenon, such as an alien god, doesn't help one to understand the underlying principle behind all phenomena, which is the first step towards opening one's mind to the nature of Reality.
Or you might take another route and boil it down to this question: "Can you ever be certain that your mind is working logically?" After all, plenty of insane people believe that they are being perfectly logical -- so how can you be sure that you aren't one of the crazy ones? And if you think you can be certain of that, why do you think so?
:-)