The cluster of puzzles and perplexities that constitute the Mind-Body-Problem of modern philosophy owes its origin to a great variety of motives and considerations. The central issue, however, may justly be located in the disputes between Dualism and Monism. The dualistic doctrines have a twofold root: Firstly, there are the mythological, animistic, theological, and religious-moral contentions as to the sharp distinction, if not actual separability, of the mental and the physical. The deeper-seated and culturally fairly widespread wishful belief in some form of survival after bodily death, as well as the exaltation of the spirit and the deprecation of the flesh in so many Eastern and Western religions and moral codes may be regarded as the emotional root of dualism. The other, scientific, root of dualism may be found in the rise of science, most prominently beginning with the seventeenth century, although at least adumbrated in ancient thought. The striking success of the method of the physical sciences was, at least historically, contingent upon a clear-cut division of the physical and the mental, and the relegation of the latter to the limbo of a sort of secondary or epiphenomenal existence. But the development of modern psycho-physics and psycho-physiology from the nineteenth century on, culminating in present-day neuro-physiology, Gestalt-psychology, psycho-somatic medicine, and cybernetics, has revived the interest in monistic interpretations. One discrepant tendency may of course be seen in the dualistic claims of the researchers in the still highly questionable fields of Parapsychology (extra-sensory perception, psychokinesis, etc.). Another and very different kind of opposition comes from philosophers of various schools who either on the basis of their metaphysical commitments or simply in the name of clear thinking insist that the physical and the mental are toto genere and irreconcilably distinct and different, so that any monistic attempts at their identification must be rejected on purely logical grounds.