 This understanding of human action has often been misappropriated by interpreters who have assumed that when Aquinas says that acts are wrongful by reason of their “undue matter” (indebita materia), he refers to an item of behavior specifiable by its physical characteristics and causal structure. So, for example, direct killing of the innocent is taken to refer to behavior whose causally immediate effect is killing, or which has its lethal effect before it has its intended good effect. But this is incompatible with Aquinas’ fundamental and consistent positions about human action. The “matter” of a morally significant act is, for him, its immediate object under the description it has in one’s deliberation: Mal. q. 7 a. 1; q. 2 a. 4 ad 5; a. 6; a. 7 ad 8. It is, in other words, not an item of behavior considered in its observable physicality as such, but rather one’s behavior as one’s objective (or the most proximate of one’s objectives), that is, as one envisages it, adopts it by choice, and causes it by one’s effort to do so. The most objective account of human action is provided by the account that is most subjective. This sound account will, however, set aside any distorted act-descriptions that one may offer others, or even oneself, as rationalizations and exculpations of one’s choice and act, but that do not correspond to what really made the option attractive, as end or as means, and so was treated, in one’s actual course of deliberation, as one’s reason for acting as one did. The immediately and foreseen lethal effect of an act of self-defense may genuinely be a side-effect of one’s choosing to stop the attack by the only available efficacious means (ST II-II q. 64 a. 7), or it may be one’s precise object (and the “matter” of one’s choice and act) because one’s (further) intent was to take lethal revenge on an old enemy, or to deter potential assailants by the prospect of their death, or to win a reward. Behaviorally identical items of behavior may thus be very different human acts, discernible only by knowing the acting person’s reasons for acting.