But our thoughts can only be accepted as a genuine insight under certain conditions. All beliefs have causes but a distinction must be drawn between (1) ordinary causes and (2) a special kind of cause called ‘a reason.’ Causes are mindless events which can produce other results than belief. Reasons arise from axioms and inferences and affect only beliefs. Bulverism tries to show that the other man has causes and not reasons and that we have reasons and not causes. A belief which can be accounted for entirely in terms of causes is worthless. This principle must not be abandoned when we consider the beliefs which are the basis of others. Our knowledge depends on our certainty about axioms and inferences. If these are the result of causes, then there is no possibility of knowledge. Either we can know nothing or thought has reasons only, and no causes.
C.S. Lewis, "'Bulverism,'" in God in the Dock (Eerdmans: 1970) 275.