 It appears, therefore, that Kant’s discussion, in § 29 of the Prolegomena, of how, by the addition of the concept of cause, we convert a mere subjective “empirical rule” into an objective law (which is “necessary and universally valid”), is not only indebted to Hume for the insight that the connection between cause and effect is synthetic rather than analytic, it is also indebted to Hume’s discussions of the problem of induction (in section 4, part 2 of the Enquiry) and of the idea of necessary connection (in section 7). Kant agrees with Hume that the idea of necessary connection is in fact an essential ingredient in our idea of the relation between cause and effect; Kant agrees, in addition, that, if all we had to go on were a purely inductive inference from observed constant conjunctions, the inference from comparative to strict universality would not be legitimate, and the presumed necessary connection arising in this way (i.e., from custom) would be merely subjective.