The Principle of Double Effect and Just War Theory

Abstract

The paper explores the relationship between the Principle of Double Effect (PDE) and Just War Theory (JWT), with emphasis on their relationship in the philosophy of Thomas Aquinas. Both PDE and JWT are of Medieval origin (the former with St. Thomas Aquinas and the latter with St. Augustine), and are classical exponents of medieval moral philosophy. The main connection between them is, however, that they can both be viewed as theories about permissible violence and harm, that is theories about when it is morally permissible to harm and possibly kill another human being. The final point of the paper is that PDE is an important element within JWT, or rather that when just war theorists manage to justify a certain types of violence they do so by extensive use of PDE. This only applies to one part of JWT, jus in bello, which concerns the actual morality of fighting, not the right to war itself. If these assumptions can be reasonably fleshed out, and if it is possible to show that PDE is of crucial importance to certain elements of jus in bello, such as methods for justifying civilian casualties, that would entail that our own moral examinations of warfare differ precisely because we either accept or don???t accept PDE as a viable and reasonable principle in normative ethics.