The theory of emotions and its development are unique among the various domains of psychological research. Until recently, this domain was completely dominated by a pure naturalism of a kind profoundly foreign to other domains of psychological investigation. These other domains have shifted to purely naturalistic theories only with the emergence of behaviorism and similar behavioristic research traditions. Methodologically, the entire future of behaviorism is contained in the old theory of emotions, since both have developed as a reaction to the forms of spiritualistic introspective psychology that preceded them. Developing primarily on a naturalistic plane, research on the emotions stood out like a white raven from other domains of psychological research contemporary to it.