Legal philosophers usually begin their inquiries with the question “What is law?” and then allow it to shape the answers they give to all subsequent inquiries, in particular, the question of how we come to know the content of the law in a given jurisdiction. As a result, most leading theories of law include (or imply) highly implausible accounts of how we come to know the law. In this paper, I suggest reversing this order of inquiry; that is, I suggest that we take as the starting point of legal theorizing the question “how do we know the law?”. I sketch the beginning of an answer to this question – one based on the acquisition of knowledge through the reliance on testimony – and briefly explore how that account might constrain the one we give of what law is. One lesson I draw from this rudimentary account is that there is no necessary connection between knowledge of law and knowledge of its grounds. The question that animates most legal philosophy, what law is, is therefore less important than many have thought.