  Williams claims that normative reasons have an ‘explanatory dimension’. On a standard reading what he means by this is that a consideration can be a normative reason for some agent only if it is possible (i.e. would under certain conditions be the case) that the agent be motivated to act for that reason, and for it thereby to be explanatory of his acting. This first premise of the classical argument is, of course, just a statement of some version of Counterfactual Motivation internalism. Here a Counterfactual Motivation form of internalism is assumed as a conceptual truth in order to argue for an Actual State internalism; any argument proceeding from such a premise naturally has no force for those externalists who deny even the Counterfactual Motivation internalist thesis. The second premise of the argument is HTM, the Humean Theory of Motivation. If the existence of reasons entails the possibility of motivation, and the possibility of motivation entails the existence of desire, then the existence of reasons entails the existence of desire—as the Humean Theory of Reasons maintains.