  How much of a cost is this? We should distinguish between two different intuitions one might have about a thinker in the bad case. The first intuition is that a thinker in the bad case has exactly the same evidence as a thinker in the good case. Perhaps abandoning this intuition is not much of a cost (if it is any cost at all). A different intuition is the following: when a thinker in the bad case takes his experiences at face value and forms beliefs about the external world in the usual manner, those beliefs are not simply unreasonable, in the way that they would be if, for example, the thinker adopted those same beliefs on a whim, or in the absence of any reason to do so at all.  Abandoning this intuition would seem to be a much heavier price to pay.  However, it is contentious whether this intuition can be preserved on a view according to which one's evidence consists of one's knowledge. Consider, once again, a thinker in the bad case who is caused by the Demon to have a visual experience as of being in the presence of a bloodied knife. Possessing no reason to doubt that the experience is veridical, the thinker forms the belief that there is blood on the knife in the usual manner. Intuitively, this belief is at the very least better justified than it would be in the absence of the relevant visual experience. On the supposition that one's evidence consists of those propositions that one knows, we can ask: what known proposition or propositions justify this belief, to the extent that it is justified?  The proposition that there is blood on the knife is false and therefore not known. Perhaps the thinker's evidence for his belief that there is blood on the knife is the true proposition that (i) it appears that there is blood on the knife or the true proposition that (ii) my experience is as of there being blood on the  knife.[13]  However, some philosophers maintain that in typical cases of perception, one does not form beliefs about how things appear to one, or about how one's perceptual experience presents things as being: rather, in response to one's experiences, one simply forms beliefs about the external world  itself.[14]  If this is correct, then, given that knowledge requires belief, propositions like (i) and (ii) are not known because they are not believed. Hence, if this model is correct, then, on the view that one's evidence consists only of known propositions, the thinker's belief that there is blood on the knife seems to lack any  justification.[15]