In this article, I develop a general explanatory model of the liability and lesser evil justifications of harm. Despite their respective provenance in consequentialist and deontological ethics, both justifications are, at root, rich forms of the proportionality relationship between a shared set of underlying normative variables. The nature of the proportionality relationship, and the conditions under which it operates, differ between the two forms of justification. The article explores these differences in detail and the implications they have for the justification of self-defense and war.