 and as a matter of fair play. To see how this is possible, take a case involving another kind of special duty. Suppose that my mother is sick. I have an associative duty to her to provide for her care. But suppose further that I once promised my father that I would take care of my mother should the need arise. There is no good reason of simplicity to declare one of these grounds invalid. In fact, in this case the multiple grounds illuminate the fact that I owe the relevant action to different people for different reasons. The same could be true of some private variant of the public transit case. I may offer my consent to follow the rules of the bus (pay my fare, no eating or smoking, etc.) to the bus company and also owe the same thing to my fellow passengers as a matter of fair play. Fair play sometimes offers a better explanation than does consent for a duty to follow the rules. The public transit case is a representative example. Thus, the theoretical utility of fair play cannot be so easily replaced. And even if it could, fair play might still be an additional grounds for a particular duty to cooperate. he had in fact consented. I may do something which is not itself an act of consent, but which nonetheless binds me as if I had consented." Simmons, Moral Principles and Political Obligations, 89. 18 The serving conventions at some restaurants are one example, as Zhu points out. Zhu, "Fairness, Political Obligation, and the Justificatory Gap," 300. 19 Zhu could insist that I have misunderstood the conventions of the honor system in the public transit case, but again, that would not help him. For even if he has in mind a strange scenario in which skirting payment is a sign of consent to pay, there are obviously cases in which acceptance of benefits and signaling consent come apart. Suppose, for example, that Jones free-rides in a differently configured public transit system by hopping the turnstiles. He accepts the benefits of the system while offering a clear sign that he does not consent to pay. doi 10.1163/1