This Article will explore and compare the philosophical psychologies of John Stuart Mill, Sigmund Freud, and B.F. Skinner, and will survey the socio-political implications of their respective views of human nature. The Article will seek to demonstrate generally that we cannot arrive at a unified vision of the most suitable social and political order without answering fundamental questions concerning what may variously be called human nature, human psychology, or the nature of the self. More specifically, this Article will contend that liberalism is contingent upon the traditional view of the person as free, rational, characterized by a functional psychological unity with an authentic core personality which exists independent of, and perhaps prior to, social influences. It will argue that psychoanalytic thought and behaviorism, the first two of three waves of modem psychology, both reject this view of the self." Thus, to the extent that modem psychology rejects the view of the self as free, rational, unified, and authentic or original to the person, it undermines the moral-psychological case for liberalism, including the idea of the zone of personal liberty. Put simply, the case for political liberalism re- quires our adherence to this traditional view of the self.