It has been generally supposed that certain self-ascriptions, such as “I am in pain”, are infallible. This seems right. However, it is clear enough that the self-ascriptive thought is not identical to the state ascribed: the pain isn’t the same as the thought about it. This means that these are “distinct existences”, in the Humean sense. But if they are distinct existences, they can be conceived apart, which implies that they are contingently connected. So there must be worlds in which the ascription occurs without the state ascribed–which would make the ascription false. So the ascription is fallible. How then can we maintain infallibility while accepting that distinct existences are contingently connected? This is the puzzle of infallibility. How can the metaphysics (distinct existences) be made to fit with the epistemology (infallibility)?