  One might hold that criminal law’s sole function is to prevent criminal wrongdoing. Call this the preventive view. Defenders of this view need not say that we should enact whatever laws will achieve the most prevention. That \(X\) is the function of \(Y\) does not entail that we are justified in doing whatever will achieve most of \(X\) with \(Y\). That cutting is the function of knives does not entail that knife-holders are justified in cutting whatever they see. Holders of the preventive view can, in other words, accept the existence of constraints on prevention, that are not themselves justified in preventive terms (Hart 1968, 35–50). What they cannot accept is a positive case for criminal law that is not preventive.