Abstract

This paper contends that a Kantian universalizability constraint on theories of practical reason in conjunction with the possibility of collective rational agents entails the surprisingly strong conclusion that no fully agent‐relative theory of practical reason can be sound. The basic point is that a Kantian universalizability constraint, the thesis that all reasons for action are agent‐relative and the possibility of collective rational agents gives rise to a contradiction. This contradiction can be avoided by either rejecting Kantian universalizability, the possibility of collective rational agents, or the tenability of a fully agent‐relative theory of practical reason; we cannot have all three.