FECHNER, GUSTAV THEODOR. - German philosopher, b. at Gross-Särchen (Lower Lusatia) on 19 April 1801, d., after a long university career, at Leipzig on 16 November 1887. In his thought, strongly imbued with naturalistic ideas and theosophy, the most disparate principles converge, from materialism to idealism: in any case, he represented a reaction against the a priori method of the Kantians and Hegelians of the school.
In Nanno oder das Seelenlichen der Pflanzen (Leipzig 1848) he defended universal cosmic animism, which in Zend Avesta (ibid. 1851) assumes a hermetic and theosophical tone. His fame is linked to the Elemente der Psychophysik (ibid. 1860), in which he set forth the well-known psychological law that bears his name, according to which “the intensity of sensation is equal to the logarithm of the corresponding stimulus” (S = C log. R); that is, for sensation to increase in arithmetical proportion, the stimulus must increase in geometrical proportion. With it F. gave decisive development to modern experimental psychology.