Moral philosophers widely believe that it is a part of the MEANING of 'ought' statements that they imply 'can' statements. To this thesis I offer three challenges, and then I conclude on a broader methodological note. (1) Epistemological Modal Argument: for all we know, determinism is true; determinism contradicts “ought implies can”; therefore we don’t know that 'ought' implies 'can'. (2) Metaphysical Modal Argument: determinism is conceptually possible; determinism contradicts “ought implies can”; therefore “ought implies can” is not an analytic (...) truth. (3) Semantic Argument: “You ought to X” is equivalent to “Do X!”; but “Do X!” does not entail that you can X, according to leading analyses of the imperative. (4) My two modal arguments are epistemologically significant, for they illustrate a general method for refuting a whole class of argument. (shrink)