This is the real big question. We don't know how human reasoning works, but we are happy to identify, entirely based on external interaction, what is and isn't

This is the real big question. We don't know how human reasoning works, but we are happy to identify, entirely based on external interaction, what is and isn't correct human reasoning. Then someone comes up with P(A|B) is not reasoning, which seems like an internal mechanism. How do we square that?