  Some crimes are mala in se—they criminalize conduct that is morally wrongful independently of the law. Most crimes are mala prohibita—they criminalize conduct that, if morally wrongful at all, is morally wrongful partly in virtue of the fact that it is unlawful. Is (W) compatible with the existence of mala prohibita? That depends on the extent to which changes in the law can produce changes in morality. The rules of the road are the classic case. Apart from the law, it is morally wrongful to drive dangerously. Such conduct is malum in se. What we should do to conform to this moral norm is not always obvious. To help, the law puts in place rules that tell us which side of the road to drive on, when to stop, and how fast we may go. Imagine we obey these rules. In doing so, we drive more safely than we otherwise would have: we better conform to the moral norm that prohibits dangerous driving. One proposal is that it is morally wrongful to violate legal norms that have this effect: that help us better conform to moral norms that exist independently of the law (Gardner 2011, 19–21). Mala prohibita of this kind would then be compatible with (W). Of course, things are not so straightforward. Even if legal conformity generally improves our moral conformity, there may be exceptional cases in which it does not—in which we can violate the rules of the road without putting anyone in danger, or in which violation helps keep everyone safe. And there may be people for whom even the generalization is not true—whose expertise enables them to systematically violate legal norms without creating risks any greater than those created by the rest of us. Can an explanation be given of why these violations are nonetheless morally wrongful? If not, (W) implies that even morally beneficial mala prohibita—like the rules of the road—must ultimately be removed from the criminal law (Husak 2008, 103–119; Simester and von Hirsch 2011, 24–29; Wellman 2013). 