The idea of the paper is to look at the way we learn about norms, as a contribution to an understanding of their nature. It is the idea of an a posteriori ontology of norms. For it is pointless to argue about the nature of norms without paying any attention to what we do when we learn something about them or when we act with them. In its turn, the epistemic account presented here is discussed in inferential terms: different cognitive sources and inferences determine different degrees of epistemic novelty that help distinguish kinds of norms and normative systems