 To take a straightforward example: a Supreme Court justice deciding on a gay marriage law would violate public reason were she to base her opinion on God’s forbidding gay sex in the book of Leviticus, or on a personal spiritual revelation that upholding such a law would hasten the end of days. This is because not all members of society can reasonably be expected to accept Leviticus as stating an authoritative set of political values, nor can a religious premonition be a common standard for evaluating public policy. These values and standards are not public.