Directly analogous to the relation between methodology and the call for a "new philosophy," this chapter discusses the "new psychology" established by Wilhelm Wundt. From the point of view of the philosophical principles constituting the Modern and Contemporary systems of Western psychology, a pre-Kantian, (neo) Kantian, and post-Kantian grouping goes toward emphasizing the incommensurabilities found across the "Four Forces' of Contemporary psychology, the emergence of which are associated with Pavlov, Freud, Kant, and Hegel; that is, Behaviorism, Psychoanalysis, Existential-Humanistic, and the ultimately Bertalanffy's General Systems Theory. The incommensurabilities are emphasized in terms of essential distinctions regarding structure, function, and methodology, such as between natural and human science, determinism and free will, and the principles with which each "Force" establishes ontological priority.