Blackstone’s Commentaries served as the primary educational basis for newly emerging proprietary schools and, from 1817, university law schools, such as Harvard’s under the leadership of Joseph Story. Yet, natural law quickly receded from instruction, even in the teachings and writings of Story, a champion of natural-law reasoning in the common law. As American common law was worked out in the early nineteenth century, natural law was subsumed into its details; except in rare circumstances—notably in the arena of international law—common law less frequently appealed to natural law, for judges and jurists could now turn to the developing body of principles and precedents constitutive of American common law. Not that this change entailed a rejection of natural law. Story’s scholarly and judicial writings show that natural law could remain central to the animating vision and moral purpose of common law even when it was not explicitly invoked. This natural law refers to the rules of conduct humans know from their status as dependent and social beings. It is understood by reason, but better known through revelation. In its legal treatment, however, it can admit of exceptions and even be passed over in favor of other interests. Unlike in its usual interpretation by contemporary critics and proponents, then, Story’s natural law is exemplary of the ways in which natural law can be historicized and relativized, at least in its relationship to common law. Natural law was known in the historical details of the positive law: specifying duties; serving as a yardstick, from which positive laws can deviate only so far; acting as a limiting point; furnishing rights; classifying and justifying branches of the law; and forming a source of law, albeit one among several.