Two Dualisms of Practical Reason

Dualism is one way to put the traditional dualism of practical reason, i.e., that practical reason can never declare that there is greater overall reason to conform to moral, or prudential, requirements in a case of conflict between our own self-interest and our obligations to others.1 In this paper, I distinguish two methods by which one might accept Dualism. First, I discuss a substantive dualism of practical reason. This version—which, incidentally, I argue is the best interpretation of Sidgwick’s infamous dualism of practical reason—holds that Dualism is a substantive principle of practical rationality, i.e., that one is never practically irrational in conforming to either moral requirements or prudential requirements. Second, I discuss a structural dualism of practical reason, of the sort floated by David Copp.2 A structural dualism holds that it is incoherent to suggest that one could be prudentially required to φ, morally required to ψ, and