Double Effect Reconsidered: A Thomistic Reappraisal of Contemporary Accounts

Abstract: Ongoing disputes in bioethics and moral theology concerning double effect reasoning (DER) prompt a reevaluation of it—going back to its roots in Thomas Aquinas, who first considers an act with good and bad effects in his justification of killing in self-defense ( Summa theologiae II-II, q. 64, a. 7). In my analysis of this article, I will argue that Aquinas’s account contains all the basic elements found in contemporary articulations of DER. However, more recent accounts contain modifications that suggest a departure from natural teleology. I will propose revised criteria for DER that more accurately reflect Aquinas’s appreciation for natural teleology: (1) the act must be naturally ordered to the good effect, but not the bad effect, which is per accidens (the bad effect may foreseeably follow sometimes or in few cases); (2) the good effect must be intended, but the bad effect must be praeter intentionem ; (3) the act must be proportioned to the good effect, such that the chances of the bad effect occurring are not unduly increased; and (4) the act must have priority over a foregone act that would prevent the bad effect.