While adopting the distinction between justification and legitimacy noted in the previous chapter, the approach developed in this book nevertheless offers a single model for explaining both. That model – termed here “the social waiver” – sets out the basic justifying conditions for a good political society, and also demonstrates why a political society that meets those conditions can legitimately bind its citizens (in ways that it cannot bind outsiders). As we have seen, the fact that it meets those conditions could not be the (sole) reason for its legitimacy – it is only necessary, not sufficient; but, I shall argue, the same considerations underlie both the justifying conditions and the legitimating reasons. That will be the task of the first part of this chapter. The second half, extending the notion of the social waiver, returns to the issue of moral dualism discussed in chapter 1. There, it was argued only that moral dualism is not necessary to make sense of the two kinds of obligation that people have, partial and universal; this chapter sets out to show how the two kinds of obligation are related.

In his Second Treatise Locke gives the impression, at several points, that he envisages the social contract as an essentially hypothetical device.