The story of psychology's emergence as a science in the late nineteenth century is largely one of reliance on developments in western Europe from direct foundations in Greek philosophy of science. The close association of psychology's history with Western intellectual traditions flows logically from basic philosophical premises about the nature of the person, which date back to the ancient Greeks. As we shall see, the basic assumption attending the flowering of ancient Greek thought is that the person is a dualistic entity composed of body and soul – the physical and the psychical, non-physical aspects of human experience. Through a complicated and complex history, psychology entered the twentieth century as a newly founded academic discipline and heir to a Western tradition that conceived of the person in terms of physical and psychical parts. As physics and physiology studied the former aspect, so too did the psychical aspect of experience require study, and thus was defined the purview of psychology.
In a real sense, the twentieth-century systems of psychology all evolved by accepting or rejecting the ancient Greek dualistic conception. With the emergence of modern science in post-Renaissance Europe, and the gradual abandonment of theological and metaphysical explanations of the psychical aspect of human experience, the need for an empirical psychology became more and more compelling. However, as psychology was redefined by nineteenth- and twentieth-century scientific advancements, its subject-matter and methodology were repeatedly debated. The twentieth-century systems, reviewed in the second half of this book, reflected differing solutions to questions about the content and method of psychology, but they all remained within the Western intellectual heritage stemming from the ancient Greeks.
While the long intellectual link between contemporary empirical psychology and Western intellectual history is apparent, it is nevertheless the case that non-Western philosophies have given considerable attention to the nature of the person and the internal world of individual reflection. These non-Western sources of psychology's past may be considered in two ways. First, the important influence of non-Western thought on the course of Western psychology and science provided a rich resource. Indeed, we can point to certain historical periods during which contacts with Eastern intellectual and religious traditions, sometimes more advanced and often more varied than in the West, brought new or recovered achievements to Western intellectual progress.