Both William James and Sigmund Freud were active during the crisis of late-positivistic psychology. Both contributed to put on a new basis the theory and practice of psychodynamic research from different points of view. Both showed a reciprocal high esteem in their meeting at Worcester University (1909). This paper discusses their divergent outlooks about the relationship between conscience and the unconscious, involving particularly the problem of free will and necessity in the domain of the psyche. Freud's rigid faith in determinism, as stated in his sketch "Project of a Psychology" (1895), and thereafter in psycho-analytic theory and practice, seems to be less open to recent trends of research in the neuro-sciences than James' "dilemma of determinism", which founded free will rather on the basis of moral introspection than on that of experimental psychology.