 The crucial difference between Strong and Weak supervenience is the second necessity operator in Strong. An example will make the difference here vivid: weak ethical supervenience is compatible with it being a brute fact that there are both “utilitarian” possible worlds where rightness covaries uniformly with happiness maximization, and “Kantian” possible worlds, where rightness covaries uniformly with satisfying the categorical imperative. By contrast, strong supervenience denies this possibility.