Thomas Aquinas’ Theory of Double-Effect
The theory of double-effect is a development from Aquinas’ justification of killing in self-defense: ST II-II, 64, 7).
- One may never intend intrinsically evil actions, even for a good end (anti-Utilitarian).
- A good action, or at least a morally neutral action, can have two effects: a good intended, and an evil, not intended, but tolerated.
- Proportionality: the good to be achieved must outweigh the evil tolerated; one cannot allow significant evil effects for a trivial reason.