Taking philosophical principles as a point of departure, this book provides essential distinctions for thinking through the history and systems of Western psychology. The book is concisely designed to help readers navigate through the length and complexity found in history of psychology textbooks. From Plato to beyond Post-Modernism, the author examines the choices and commitments made by theorists and practitioners of psychology and discusses the philosophical thinking from which they stem. What kind of science is psychology? Is structure, function, or methodology foremost in determining psychology's subject matter? Psychology, as the behaviorist views it, is not the same as the psychoanalyst's view of it, or the existentialist's, so how may contemporary psychology philosophically-sustain both pluralism and incommensurability? This book will be of great value to students and scholars of the history of psychology.