This article argues that the natural law common good is the best candidate value to ground a direct justification of political authority. The common good is better placed than rival values to ground a direct justification for three related reasons. First, the common good is the right kind of value to serve in a justification of political authority insofar as it is a reason for action which provides a convincing answer to the fundamental question ‘why have authority at all?’ Second, the common good allows for a justification of political authority that pertains to a complete political community rather than subjects taken individually. Third, the common good allows for a reconciliation of two apparently conflicting features of political authority: (1) its ultimate role is to promote the good of individuals and (2) it can require the subordination of the good of the individual to the good of the community.