 It is indeed crucially important to distinguish between the general principle of causality Kant establishes in the Second Analogy and particular causal laws. It is equally important that particular causal laws, for Kant, are (at least for the most part) synthetic a posteriori rather than synthetic a priori. It does not follow, however, that Kant agrees with Hume about the status of synthetic a posteriori causal laws. On the contrary, Kant (as we have seen) clearly states, in § 29 of the Prolegomena (the very passage where he gives his official “answer to Hume”), that there is a fundamental difference between a mere “empirical rule” (heat always follows illumination by the sun) and a genuine objective law (the sun is through its light the cause of heat) arrived at by adding the a priori concept of cause to the merely inductive rule. Any law thus obtained is “necessary and universally valid”, or, as Kant also puts it, we are now in possession of “completely and thus necessarily valid rules”. In such cases (A91/B124): 