 As noted earlier, there are various versions of liberal political philosophy. All of them, however, are committed to a conception of political legitimacy in which political power and authority is justified only if such authority is acceptable to all citizens bound by it (see Rawls 1993, 144–50). This connects to a broader view of the foundations of value that at least some liberal theorists present as central to that tradition. That is the claim that values are valid for a person only if those values are or can be reasonably endorsed by the person in question. By extension, principles guiding the operation of institutions of social and political power — what Rawls calls the institutions of the basic structure (Rawls 1993, 258) — are legitimate only if they can be endorsed in this way by those subject to them. In this way, liberalism (in most of its forms) is committed to what some have called the “endorsement constraint” (Kymlicka 1989, 12f, R. Dworkin 2000, 216–18).