 Section 4 of the Enquiry is entitled “Sceptical Doubts Concerning the Operations of the Understanding”. In part 1 of this section (as we have already seen) Hume maintains that the idea of the effect is never contained in the idea of the cause (in Kant’s terminology, the relation is not analytic), and thus, according to Hume, it is never knowable a priori. We therefore need experience in the Humean sense in order to make any causal claims—that is, the observation of an event of one type A constantly followed by an event of another type B. Otherwise (as we have also seen) any event could follow any other (EHU 4.10; SBN 29): 