Philip Soper (b. 1942) is an American legal and moral philosopher. In A Theory of Law (1984), Soper develops novel accounts of the law’s normative force and of political obligation. Rawls draws on this work in his accounts of the common good idea of justice and legal systems in decent societies (CP 545, 546; LP 66, 67, 72; PL 109).

Soper argues that the law has normative force only when public officials sincerely believe the law serves justice or the common good. When officials sincerely believe the law does this for all, citizens have reason to respect it. This is so, even when any citizen might reasonably reject the official conception of justice or the common good as suboptimal or wrong-headed. This respect for the law amounts to a duty to defer when officials enforce the law.

Rawls does not define legal systems, but follows Soper as to when and how legal systems impose bona fide duties and obligations (LP 65–66). Like Soper, he holds that officials must be willing to defend, publicly and in good faith, laws requiring or forbidding conduct (LP 67). For Rawls, this means officials must reasonably see their law as consistent with their common good conception of justice.