When a legal rule requires us to drive on the right, notarize our wills, or refrain from selling bootleg liquor, how are we to describe and understand that requirement? In particular, how does the logical form of such a requirement relate to the logical form of other requirements, such as moral requirements, or the requirements of logic itself? When a general legal rule is applied or distinguished in a particular case, how can we describe that process in logical form? Such questions have come to preoccupy modern legal philosophy as its methodology, drawing on the philosophy of logic, becomes...