 There are two major difficulties facing a view of this sort. First, it is not clear how one belief is supposed to reduce the warrant for another. Suppose that I correctly believe that I have a headache and that my belief is, in an intuitive sense, absolutely certain. The first condition of Klein’s account is satisfied: the belief is warranted in virtue of my experiencing the headache. But is the second condition also satisfied? That is, would I be warranted in denying, say, the proposition that I do not in fact have a headache? If this were to be a belief added to my belief system, I would of course have contradictory beliefs. Would that entail that the warrant for both beliefs should be diminished? If the answer is yes, then my belief that I have a headache is not absolutely certain. Moreover, it is hard to see how any belief could then be absolutely certain, given that we can always add to our belief systems the contradictory of any of our beliefs. If the answer is no, however, there should be some explanation for why the proposition that I do not have a headache can be denied. Presumably, the explanation would have something to do with my experiencing the headache. But then what explains the certainty of the belief is the fact that it is grounded in the experience; the belief’s being subjectively immune to doubt is merely a consequence of its certainty, and not the explanation for it. This would mean that the focus of the view has shifted from subjective immunity to doubt to some sort of special warrant. How there could be such a special warrant, though, would need an account. To see the point more clearly, notice that subjective immunity to doubt will be possible only in cases where the subject’s belief is (intuitively) absolutely certain. For any belief b that is less than certain, the following belief could be added to the subject’s belief system: the warrant for b could be misleading. That belief would reduce the subject’s warrant for b (even if only slightly) were it to be added to her belief system, but it is not a proposition the subject can deny without being absolutely certain that b is true. The upshot, then, is that subjective immunity to doubt is not well-suited to playing a role in an account of certainty. Instead, it looks as though our understanding of subjective immunity to doubt depends on a prior grasp of what certainty is.