[Psychological strength and tension according to Pierre Janet]

Janet's psychological studies are focused on behavior. In this objectival perspective, action appears to be underlain by two parameters, i.e. strength and tension. The latter is connected with a hierarchic organization of the psychological facts which are topped by the reality function. The different stages of the development of this theory are exposed. The author emphasizes the first works about hysteria and psychasthenia. The later studies on tendencies and sentiments are more concisely mentioned.