  It is possible to imagine a world in which the law gets its way—in which people uniformly refrain from criminal conduct. Obviously enough this is not the world in which we live. Imagine \(D\) is about to \(\phi\). If \(\phi\)ing is a crime, reasonable force may permissibly be used to prevent \(D\) \(\phi\)ing. Police officers and private persons alike have powers to arrest \(D\), and reasonable force may permissibly be used to make arrests effective.