Double-Effect Reasoning: Doing Good and Avoiding EvilT. A. Cavanaugh defends double effect reasoning (DER), also known as the principle of double effect. DER plays a role in anti consequentialist ethics (such as deontology), in hard cases in which one cannot realize a good without also causing a foreseen, but not intended, bad effect (for example, killing non combatants when bombing a military target). This study is the first book length account of the history and issues surrounding this controversial