In this Lecture I shall discuss the reasons that officials and citizens should rely upon in American politics. In recent years, various theorists have claimed that people in liberal democracies should rely in politics on public reasons, reasons that are accessible to all citizens. Others have objected that such a counsel is unreasonable, if not incomprehensible. I shall concentrate on two facets of this issue. First, does the law exemplify a structure of public reasons – that is, do judges deciding cases draw on a stock of public reasons that is narrower than all the reasons one might give for a particular result? My second inquiry concerns the status of natural law – long claimed by adherents to be a source of reasons of universal power,...