In his 1874 Psychology, Brentano proceeds to a revision of Fechner’s psychophysics. Fechner’s formula must be simplified, but Brentano’s criticism is not destructive. In fact, like any other mental activity, sensations do admit of a measurable intensity. Later Brentano took back this whole stance and developed a new doctrine of sensory perception. Accordingly, intensity must be completely reduced to spatiality and thus pertains exclusively to sensory appearances. As a consequence, despite Brentano’s understatement in his 1911 book on the classification of mental activities, a wide portion of his 1874 Psychology becomes untenable for him. Brentano’s new doctrine of sensory perception was unsuccessful, and failed to convince even his closest pupils. The best explanation for its adoption is that Brentano considered it compatible with the physiology of Hermann Helmholtz and the law of specific energy
