 The definition of law offered by Aquinas in ST I-II q. 90 a. 4 is: “an ordinance of reason for the common good of a [complete] community, promulgated by the person or body responsible for looking after that community.” It is by being intended for common good that law appeals to its subjects’ reason, and gives them reason for regarding the law as authoritative and obligatory, morally as well as legally. Even when its subjects or some of them would have made or preferred a different determinatio, a different way of pursuing communal benefit, the rulers’ intent to promote common good supports and is supported by their claim to rulership. Only if they have such intent can they instantiate the central case of government.