 But if our only access to the external world is mediated by potentially misleading perceptual appearances, we ought to have some assurance that the appearances we are relying on are not of the misleading variety. And here is where all the trouble arises, for it seems that there is no way we could have any evidence for the reliability of perception (i.e., perceptual appearances) without relying on other perceptions. We have empirical reason, for example, to think that science is not yet capable of stimulating brains in a very precise way, but appealing to this to rebut the possibility of brain-in-a-vat scenarios seems blatantly question begging. At the heart of the problem of the external world is a skeptical argument I will refer to as “PEW” and which I reconstruct in what follows. I have named the premises, as we will want to discuss them individually.