Defensive harm is subject to both a proportionality and necessity constraint. In what follows I precisify, explain, and unify these two constraints. I argue that they express the very same moral demand, only at different levels of generality—specifically, the demand that an attacker not be made to bear more cost to avert their attack than they would be required to take on themselves.

Philosophy &Public Affairs, Volume 51, Issue 1, Page 33-59, Winter 2023.