" Life may be something not only ultra-terrestrial, but even immaterial, something outside our present categories of matter and energy; as real as they are, but different, and utilizing them for its own purpose " (Life and Matter, p. 198), The theory of psychophysical parallelism recognizes that while there is a correspondence between mental and material phenomena, changes in the mind and changes in the brain, the former cannot be explained by the latter, as the transition from the one to the other is unthinkable.
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.
On the fundamental question, however, of the psychophysical connexion and the derivation of mind from matter, his utterances are neither clear nor consistent.
Huxley (Science and Culture) and Shadworth Hodgson (Metaphysic of Experience and Theory of Practice), must be distinguished from that of the psychophysical parallelism, or the "double aspect theory" according to which both the mental state and the physical phenomena result from a so-called "mind stuff," or single substance, the material or cause of both.
Accordingly, he calls these and all other processes " psychophysical "; and as he recognized two parallel energies, physical and psychical, differing only as outer and inner aspects of the same energy, he called this " psychophysical energy."