 In § 36 of the Prolegomena (after he has presented his official “answer to Hume” in § 29) Kant addresses the question of the relationship between particular empirical laws and the a priori principles of the understanding under the title “How is nature itself possible?” Nature in the material sense is “the totality of all appearances” given in space and time (4, 318; 69). Nature in the formal sense is “the totality of rules under which all appearances must stand if they are to be thought as connected in an experience” (4, 318; 70). In answering the question of how nature in the formal sense is possible Kant proceeds to distinguish between “empirical laws of nature, which always presuppose particular perceptions” and 