 How do we explain someone’s believing something like M, P or S? We normally need to know her reasons for believing it to be true, which we can then go on to assess as good or bad reasons for such a belief. Either way, we typically take her reasons—and the reasoning associated with them—to explain her belief, which is why we engage seriously with her reasons as such in critical discussion, and go on to inquire into their merits. If, for example, we ask a person why she believes M, and she cites a proof she has found convincing, showing that for any natural number n &gt; 1 there is at least one prime number between n and 2n, we normally take this as a sufficient explanation for why she believes M. What we do not normally do is to appeal directly to independent causes, such as evolutionary or other biological or psychological influences to explain people’s beliefs in these areas. Such independent explanations for beliefs can sometimes be correct, as in the case of someone given a post-hypnotic suggestion, in which case we may regard her judgment as merely caused and the reasons offered as mere rationalization. But this is not the norm.