Legitimacy: The Liberal Principle of Legitimacy

In a democracy, political power is always the power of the people as a collective body. In light of the diversity within a democracy, what would it mean for citizens legitimately to exercise coercive political power over one another? Rawls's test for the acceptable use of political power in a democracy is his liberal principle of legitimacy:

Our exercise of political power is fully proper only when it is exercised in accordance with a constitution the essentials of which all citizens as free and equal may reasonably be expected to endorse in the light of principles and ideals acceptable to their common human reason. (PL, 137)

According to this principle, political power may only be used in ways that all citizens can reasonably be expected to endorse. The use of political power must fulfill a criterion of reciprocity: citizens must reasonably believe that all citizens can reasonably accept the enforcement of a particular set of basic laws. Those coerced by law must be able to endorse the society's fundamental political arrangements freely, not because they are dominated or manipulated or kept uninformed.

The liberal principle of legitimacy intensifies the challenge of legitimacy: how can any particular set of basic laws legitimately be imposed upon a pluralistic citizenry? What constitution could all citizens reasonably be expected to endorse? Rawls's answer to this challenge begins by explaining what it would mean for citizens to be reasonable.