Ego Depletion and the Humean Theory of Motivation

By what capacities do human beings engage in intentional action? Humeans about motivation claim that the source of all action is desire. Volitionalists claim that action has two distinct sources, one in the will and one in desire. Recent work suggests that volitionalism has some empirical support. Roy F. Baumeister and colleagues have argued for a phenomenon called “ego depletion”. They argue that some aspect of the self exerts volition in a number of different contexts. The main evidence for this claim is that experimental subjects who engage in acts of self-regulation are less likely to engage in similar actions on later tests. The evidence calls for a reformulation of the Humean theory, not a rejection of it. And the reformulation is one that still has interest for metaethics. Many philosophers are interested in the Humean theory of motivation because they believe that it has implications for the correct theory of normative practical reasons. Here I argue that if the Humean theory of motivation was ever a threat to the objectivity of morality, it still is.