The concept of second nature promises to provide an explanation of how nature and reason can be reconciled. But the concept is laden with ambiguity. On the one hand, second nature is understood as that which binds together all cognitive activities. On the other hand, second nature is conceived of as a kind of nature that can be changed by cognitive activities. The paper tries to investigate this ambiguity by distinguishing a Kantian conception of second nature from a Hegelian conception. It argues that the idea of a transformation from a being of first nature into a being of second nature that stands at the heart of the Kantian conception is mistaken. The Hegelian conception demonstrates that the transformation in question takes place within second nature itself. Thus, the Hegelian conception allows us to understand the way in which second nature is not structurally isomorphic with first nature: It is a process of ongoing selftransformation that is not primarily determined by how the world is, but rather by commitments out of which human beings are bound to the open future.