In philosophy he began with a strong predilection for the physical side of psychology, and at an early age he came to the conclusion that all existence is sensation, and, after a lapse into noiimenalism under the influence of Fechner's Psychophysics, finally adopted a universal physical phenomenalism.
It becomes necessary, therefore, to determine how far Fechner derived his psychophysics from experience, how far from fallacies of inference, from his romantic imagination and from his theosophic metaphysics, which indeed coloured his whole book on psychophysics.
By his psychophysics he meant the exact doctrine of the relations of dependency between physical and psychical.
Having satisfied himself in what he called " outer psychophysics," that the stimulus causes only the nervous process and not sensation, he passed to what he called " inner psychophysics," or the theory of the relation between nervous and psychical processes.
Fechner first confused physics and metaphysics in psychophysics, and next proceeded to confuse them again in his work on evolution (Einige Ideen zur SchOpfungs and Entwicklungs-geschichte der Organismen, 1873).
When the later reaction to Kant arose against both Hegelianism and materialism, the nearly contemporary appearance of Fechner's Psychophysics began to attract experimental psychologists by its real as well as its apparent exactness, and both psychologists and metaphysicians by its novel way of putting the relations between the physical and the psychical in man and in the world.
For a time, under the influence of Fechner's Psychophysics, he thought that Nature has two sides, a physical and a psychological, and added that all atoms have feeling.
But his main sympathy was with Fechner, the gist of whose " inner psychophysics " he adopted, without, however, the hypothesis that what is conscious in us is conscious in the all-embracing spirit of God.
His phenomenalism also compelled him to give a more modified adhesion to Fechner's " outer psychophysics."