  This line of argument has not yet received much attention; opponents may reasonably question whether motivation by reasons must always be voluntary (this seems implausible in the case of theoretical reasons, or reasons for belief, for example—see section 2.2 below for this analogy), and also whether voluntary behavior must be caused by desire.  For yet a different promising argument for internalism on the basis of the connection between reasons and motivational capacities, see section 4 of (Markovits 2011).