What if ideal advice conflicts? A dilemma for idealizing accounts of normative practical reasons

I present a dilemma for the leading anti-realist theory of practical normativity: idealizing reasons subjectivism. According to this view, an agent’s reasons for action are grounded not in her actual pro-attitudes, but in those she would have if fully non-normatively informed and ideally structurally rational. I argue that the view assumes that, for any agent with irrational attitudes, the relevant idealizing process yields a uniquely rational set. This assumption is false, and its failure generates two puzzles for idealizing subjectivism: one about which practical reasons exist and another about how much normative weight they have. Attempts to solve the second puzzle confront idealizing subjectivists with a dilemma. They must hold either that the weights of an agent’s reasons are arbitrarily determined by the attitudes of just one of her many ideal counterparts or that they are determined by some amalgamation of those counterparts’ attitudes that it would be positively irrational for any agent to possess. Both horns are deeply implausible. The dilemma therefore constitutes a powerful but as-yet unnoticed objection to idealizing subjectivism.