 Is it really true, however, that, compared with perception, introspection is in some way special? Critics of foundationalism have argued that introspection is not infallible. Might one not confuse an unpleasant itch for a pain? Might I not think that the shape before me appears circular to me when in fact it appears slightly elliptical to me? If it is indeed possible for introspection to mislead, then it is not clear in what sense introspection can constitute its own success, provide certainty, or even incorrigibility. Yet it also isn’t easy to see either how, if one clearly and distinctly feels a throbbing headache, one could be mistaken about that. Introspection, then, turns out to be a mysterious faculty. On the one hand, it does not seem to be an infallible faculty; on the other hand, it is not easy to see how error is possible in many specific cases of  introspection.[56]