In this paper I extend the case for a necessitation account of particular laws in Kant's philosophy of science by examining the relation between reason's hypothetical use in the Appendix to the Transcendental Dialectic and the legitimate hypotheses identified in the Doctrine of Method. Building on normative accounts of reason's ideas, I argue that reason's hypothetical use does not describe the connections between objects and their grounds, which lie beyond the reach of the understanding, but merely prescribes the relations between (...) appearances and their conditions, for which the understanding must seek. A legitimate hypothesis, I suggest, is a proposition we hold to be true that fills in one or several of those relations. The problematic character of hypotheses requires that we evaluate our reasons for holding them to be true. While natural modality is grounded in the nature of things, which cannot be fully known, our reasons for assent can and must be grounded on features of objects that are epistemically available to us. (shrink)