Moral properties are explained by other properties. And moral principles tell us about moral properties. How are these two ideas related? In particular, is the truth of a given moral principle part of what explains why a given action has a given moral property? I argue “No.” If moral principles are merely concerned with the extension of moral properties across all possible worlds, then they cannot be partial explainers of facts about the instantiation of those properties, since in general necessitation does not suffice for explanation. And if moral principles are themselves about what explains the moral properties under their purview, then by their own lights they are not needed in order to explain those moral properties’ instantiation—unless, that is, the principles countenance an objectionable form of metaphysical circularity. So moral principles cannot explain why individual actions have moral properties. Nor, I also argue, can they explain why certain other factors explain why those actions have the moral properties that they do, or in some other way govern or mediate such first-order explanations of particular moral facts. When it comes to the explanation of an individual action’s specific moral features, moral principles are explanatorily idle.