Nagel has been highly influential in the related fields of moral and political philosophy. Supervised by John Rawls, Nagel has been a long-standing proponent of a Kantian and rationalist approach to moral philosophy. His distinctive ideas were first presented in the short monograph "The Possibility of Altruism," published in 1970. That book seeks by reflection on the nature of practical reasoning to uncover the formal principles that underlie reason in practice and the related general beliefs about the self that are necessary for those principles to be truly applicable to us. Nagel defends motivated desire theory about the motivation of moral action. According to motivated desire theory, when a person is motivated to moral action it is indeed true that such actions are motivated – like all intentional actions – by a belief and a desire. But it is important to get the justificatory relations right: when a person accepts a moral judgment he or she is necessarily motivated to act. But it is the reason that does the justificatory work of justifying both the action and the desire. Nagel contrasts this view with a rival view which believes that a moral agent can only accept that he or she has a reason to act if the desire to carry out the action has an independent justification. An account based on presupposing sympathy would be of this kind.