 Here Mill defines wrongness and, by implication, duty, not directly in terms of the nature of the action or its consequences but indirectly in terms of appropriate responses to it. He appears to believe that one is under an obligation or duty to do something just in case failure to do it is wrong and that an action is wrong just in case some kind of external or internal sanction—punishment, social censure, or self-reproach—ought to be applied to its performance. This test distinguishes duty from expediency (V 14, 15). Not all suboptimal or inexpedient acts are wrong, only those to which one ought to apply some sort of sanction (at least, self-reproach).