Ethics and the limits of practical reason (Immanuel Kant, David Hume, Christine Korsgaard, Thomas Nagel)

My dissertation examines the intersection of theories of practical reason and attempted justifications of morality. While criticizing rationalist, or Kantian, justifications of morality, I argue for a comprehensive Humean theory of practical reason. Rationalist justifications of morality attempt, based on considerations of what it is to be a practical agent, to show that all agents must take the interests of others into account, and hence must act morally. The rationalists I consider, including Thomas Nagel, Alan Gewirth, and Christine Korsgaard, all argue that reasons have a lawlike form requiring each agent to take the reasons of every agent into account. In reality, the lawlike form of reasons only requires agents to admit that others in similar circumstances have similar reasons. I take advantage of resources from these failed rationalist projects in justifying a comprehensive Humean theory of practical reason. In contrast to previous Humean views my theory not only provides a better foundation for its principles, but it also deals more thoroughly with notions of authority and obligation. From the traditionally rationalist concept that reasons are rule-based, things we can be right or wrong regarding, I argue that an agent's desires constitute reasons, excepting cases where a desire conflicts with an agent's practical identities. Based on a notion of reasons as considerations in favor of an action, I then argue for a strong separation of reasons and obligations. I conclude that practical reason is limited in scope such that each agent need consider only his or her own reasons, a limit that precludes the success of rationalist justifications of morality.