 Even if there were sufficient intuitive support for [P1], defending this argument by such means would contravene both strands of the non-self-undermining constraint (Pust 2001). According to [P1], S’s non-introspective belief that p is justified only if the proposition believed plays a role in the best explanation of S’s mental states. No demonstration of explanatory relevance is involved in the two methods of justifying [P1] just discussed. Rather, each approach would take the mere fact that the principle is the content of an intuition or best explains the content of a set of particular intuitions (i.e., intuiteds) as sufficient for justified belief in that principle. This is to treat intuiteds as supporting evidence for a principle allowing only intuitings to count as evidence. Moreover, since [P1] states a necessary condition for the justified acceptance of any proposition not about the occurrence of an observation or intuition, acceptance of [P1] itself is justified only if it satisfies the very requirement it articulates. Unfortunately, because [P1] is a normative proposition about when a belief is justified, it is difficult to see how its truth could play any role in the explanation of the occurrence of any of our experiences or intuitions. However, if [P1] does not satisfy [P1], then, if [P1] is true, we cannot be justified in believing [P1].