It is true, also, that on its idealistic side the philosophy of Leibnitz is the source of many current views of panpsychism, of psychophysical parallelism as well as of the.
He accepts psychophysical parallelism in the sense that every psychical process has a physical accompaniment, every physiological function has a psychical meaning, but neither external stimulus nor physiological stimulus is cause of a psychical process, nor vice versa.
Clifford (q.v.) was working out the hypothesis of psychophysical parallelism to a conclusion different from that of Lewes, and more allied to that of Leibnitz, the prime originator of all these hypotheses.
He agrees with Fechner that physical process of nerve and psychical process of mind are really the same psychophysical process as appearing on the one hand to an observer and on the other hand to one's own consciousness; and that physical phenomena only produce physical phenomena, so that those materialists and realists are wrong who say that physical stimuli produce sensations.
Fechner (1801-1887) affords a conspicuous instance of the idealistic tendency to mysterize nature in his Panpsychism, or that form of noumenal idealism which holds that the universe is a vast communion of spirits, souls of men, of animals, of plants, of earth and other planets, of the sun, all embraced as different members in the soul of the world, the highest spirit - God, in whom we live and move and have our being; that the bodily and the spiritual, or the physical and the psychical, are everywhere parallel processes which never meet to interact; but that the difference between them is only a difference between the outer and inner aspects of one identical psychophysical process; and yet that both sides are not equally real, because while psychical and physical are identical, the psychical is what a thing really is as seen from within, the physical is what it appears to be to a spectator outside; or spirit is the self-appearance of matter, matter the appearance of one spirit to another.
Though no noumenalist, in many details he is with noumenalists; with Fechner in psychophysics, in psychophysical parallelism, in the independence of the physical and the psychical chains of causality, in reducing physical and psychical to a difference of aspects, in substituting impulse for accident in organic evolution, and in wishing to recognize a gradation of individual spiritual beings; with Schopenhauer and Hartmann in voluntarism; and even with Schelling and Hegel in their endeavour, albeit on an artificial method, to bring experience under notions, and to unite subject and object in one concrete reality.
Nevertheless, largely under the influence of the exaggeration of the conservation of energy, many psychologists - Wundt, Paulsen, Riehl, Jodl, Ebbinghaus, Miinsterberg, and in England Lewes, Clifford, Romanes, Stout - have accepted Fechner's psychophysical parallelism, as far at least as men and animals are concerned.
At the same time Fechner would not have us suppose that the two sides are equal; according to him, the psychical, being the psychophysical as viewed from within, is real, the physical, being the psychophysical viewed from without, is apparent; so in oneself, though nervous process and psychical process are the same, it is the psychical which is the reality of which the nervous is mere appearance; and so everywhere, spirit is the reality, body the appearance of spirit to spirit.
The theory of psychophysical parallelism has been subjected to a rigorous examination in James Ward's Naturalism and Agnosticism, part iii., in which the argument that mind cannot be derived from matter is convincingly presented.
He disagrees with Fechner's hypothesis of a world-soul, the highest spirit, God, who embraces all psychophysical processes.