 The basis of Rawls’s theory in necessity becomes evident if we explore what it might be for a just institution to “apply to us”. An Institute for the Advancement of Philosophers cannot benefit us, however justly, and then demand that we pay its dues (Simmons 1979: 148). If so, it looks as if we need to accept the benefits provided by a given institution before the institution in question can be said to “apply to us”. But that is to transform a natural duty account into a weakly voluntarist one like fairness (see above,  §4.2).  One way to diagnose the force of such counterexamples is to notice that, although operating justly, the Institute is not something whose activities are required by justice: they are optional, not necessary (Waldron 1993).