Can Hybrid Voluntarism Solve the Indeterminacy Problem of the Reasons Responsiveness Account of Rationality?

The conception of rationality as Reasons Responsiveness (RR) has seen a revival in the literature. However, RR faces the indeterminacy problem: an agent may be instrumentally irrational even without failing to respond correctly to reasons. Reasons do not conclusively determine choice, but this should not be possible on RR. Hybrid Voluntarism (HV), which is supposed to apply particularly to cases where “reasons run out”, may be a solution. According to Ruth Chang, we can create will-based reasons through commitment if the given reasons balance. HV is attractive since it seems to explain instrumental irrationality and preserve RR’s distinctive appeal. In this paper, I argue that HV fails to save RR in the face of indeterminacy. I first suggest that we distinguish between overdetermination and underdetermination and then show that while RR may solve the former, it fails with the latter. Therefore, we are still left with a case of irrationality without a failure to respond correctly to reasons.