 To get an intuitive grasp on necessity and proportionality, note that if someone threatens my life, then killing her would be proportionate; but if I could stop her by knocking her out, then killing her would be unnecessary, and so impermissible. The necessity and proportionality constraints have the same root: with few exceptions (perhaps when it is deserved), harm is intrinsically bad. Harms (and indeed all bads) that we cause must therefore be justified by some positive reason that counts in their favour—such as good achieved or evil averted (Lazar 2012a). Both the necessity and proportionality constraints involve comparing the bads caused by an action with the goods that it achieves. They differ only in the kinds of options they compare.