Abstract
According to legal anti-positivism, legal duties are just a subset of our moral duties. Not every moral duty, though, is legal. So what else is needed? This article develops a theory of how moral duties come to be law, which I call the constitutive reasons account. Among our moral reasons are legal reasons-and those reasons make moral duties into legal duties. So the law consists of moral duties which have, as one of their underlying reasons, a legal reason. Such legal reasons arise from a relationship with the body for which it is the law of. The legal reasons in America, then, are the moral reasons flowing from a relationship with the United States. These reasons include consent, democracy, association and fair play. They are law's constitutive reasons. By looking for them, we can better explain why some moral duties form part of the law, while others do not.