  Humeans have defended their position in several ways, but contemporary debate has focused in large part on an argument developed by Bernard Williams. Williams argues that only Humeanism can explain the relation between reasons and motivation: if one has a reason to act, then one can act for that reason, Williams holds. But this is only guaranteed if having a reason to act involves having a desire. Hence reasons to act depend on the existence of desires (Williams 1981). Taking a somewhat different approach, Mark Schroeder argues that, when properly formulated, Humeanism simply fits best with our range of intuitions about what reasons there are to act and the ways in which these reasons are or are not contingent on facts about our psychologies (Schroeder 2007).