  Counterfactual Motivation views, however, can adopt either direction of explanation, and a variety of philosophers insist that the existence of reasons explains the relevant facts about motivation rather than vice versa. Consider the popular thesis that if there is a reason for someone to do something, then necessarily if she is fully rational she will be motivated to do it. The most trivial account of this kind suggests that ‘fully rational’ simply means motivated by all one’s reasons. If this is the truth in internalism, however, it places no constraints whatsoever on what can and cannot be an agent’s practical reason; for this reason it is often called an externalist thesis. But the explanatory priority of reasons over motivation can also yield a nontrivial version of internalism. Consider again the thesis appealing to a condition of full rationality. If by ‘rationality’ we mean a substantive psychological capacity involving particular desires or dispositions that enable us to respond to reasons, then we have a form of internalism that places substantive constraints on what can and cannot be a reason. For example, Christine Korsgaard (1986) advocates such a nontrivial version of internalism, taking the counterfactual about motivation under the condition of rationality to be explained by a substantive (non-trivial) account of practical rationality. According to Korsgaard, an agent is only rational if she is consistently motivated in accordance with some general principles that provide her conception of her practical identity. Given this account of rationality, the internalist thesis above tells us that only those considerations that would motivate such a principle-governed agent can be reasons for her to act.