  A connection is then forged between voluntary behavior and desire. Arguably, a behavior is only voluntary if it is caused by being aimed at. On one theory of desire, aiming at p entails desiring something (either p itself, or something to which p is taken to be a means). It follows that a rational agent’s recognition of a reason entails the presence of a relevant desire. This does not yet rule out externalism, which is compatible with this result if any of a number of different claims are true. The internalist can try to close off these escapes, however. (i) One possible externalist solution is that being rational involves having certain desires; the internalist can argue in response that rationality is rather a procedural virtue which doesn’t necessarily involve having any particular desires. (ii) Another solution is to suggest that a rational agent’s ability to recognize reasons is limited by her desires; the internalist can plausibly respond that being (ideally) rational is, by definition, to be able to recognize all one’s reasons. (iii) Perhaps most promisingly, an externalist can suggest that a rational agent can respond voluntarily to her reasons by virtue of their causing her to have a new desire (Darwall 1983). The internalist may counter by arguing that because we cannot desire at will, the causation of such a desire would be a nonvoluntary response to the recognition of a reason, and therefore any behavior motivated by that desire—even if voluntary—would not qualify as a voluntary response to the reason.