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.