Aquinas restricts coercive power to proper authorities because of the good involved; it is not merely a private good but a shared good or the community. Only the community itself, or its representatives, can order to this good.
160 why is the power to coerce limited to the proper authorities? Without an answer to this question, the position attributed to Suarez cannot explain the force of the moral ought. It can claim that law is a certain kind of command, and it can claim that command imposes an external necessity upon the will. It will be unable to explain, however, how this external necessity is any different from a bully or a robber.
Aquinas restricts coercive power to proper authorities because of the good involved; it is not merely a private good but a shared good or the community. Only the community itself, or its representatives, can order to this good.1 If we are to make the case for Suarez, then, we must investigate how a shared good might give rise to moral obligation.
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1 I-II, 90,3.
