Kant agrees with Hume that necessary connection is an essential ingredient in the idea of the relation between cause and effect.

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