The idea of a social contract as the basis for morality or political principles goes back a long way—there is, for example, a brief statement of it in Plato's Republic. More notably, the great writers on political and moral philosophy of the 18th century were contractarians. In our own time, John Rawls's work is regarded, both by him and those who are familiar with his writings, as falling within the general tradition of social contract theory, while David Gauthier's “morals by agreement” present an elaboration of the principles of contractarianism.

Inasmuch as contractarianism has specific reference to a theory about the foundations of moral and political philosophy, its relation to libertarianism is somewhat indirect. Libertarianism is a theory regarding the general principles of justice. The underlying ...