 As the previous sentence suggests, obligations are also duties. That is true, at any rate, when the obligation in question is political obligation. To be sure, some philosophers claim to have uncovered differences between obligations and duties, the most important of which is that obligations must be voluntarily undertaken or incurred, but duties need not be (e.g., Brandt 1964; Hart 1958). The obligation to keep a promise or fulfill a contract, for example, arises only when one has done something that generates the obligation – made a promise or signed a contract – but the duties of charity and truth telling supposedly fall on us regardless of what, if anything, we voluntarily commit to do. John Rawls relies on this distinction when he argues that most citizens of a reasonably just political society have no general obligation to obey its laws, even though they do have a “natural duty” to support just institutions – a duty he thinks has the general effect of requiring them to obey (Rawls 1999, p. 97). For the most part, however, the alleged distinction between obligation and duty has played no significant role in the debates over the supposed moral responsibility to obey the law. To invoke the distinction here would run counter to the tendency in both ordinary language and contemporary philosophical discussion to use the terms interchangeably, as when we speak of the “duty” to keep a promise or an “obligation” to tell the truth. This essay will proceed, then, like almost everything written on either side of the question, on the understanding that a political obligation, if it exists, is a moral duty to obey the law (but note the elaboration of this point in §2.3).