The German experimental psychologist Gustav Theodor Fechner (1801-1887) founded psychophysics and formulated Fechner's law, a landmark in the emergence of psychology as an experimental science.

Gustav Theodor Fechner was born on April 19, 1801, at Gross-Särchen, Lower Lusatia. He earned his degree in biological science in 1822 at the University of Leipzig and taught there until his death on Nov. 18, 1887. Having developed an interest in mathematics and physics, he was appointed professor of physics in 1834.

About 1839 Fechner had a breakdown, having injured his eyes while experimenting on afterimages by gazing at the sun. His response was to isolate himself from the world for 3 years. During this period there was an increase in his interest in philosophy. Fechner believed that everything is endowed with a soul; nothing is without a material basis; mind and matter are the same essence, but seen from different sides. Moreover, he believed that, by means of psychophysical experiments in psychology, the foregoing assertions were demonstrated and proved. He authored many books and monographs on such diverse subjects as medicine, esthetics, and experimental psychology, affixing the pseudonym Dr. Mises to some of them.

The ultimate philosophic problem which concerned Fechner, and to which his psychophysics was a solution, was the perennial mind-body problem. His solution has been called the identity hypothesis: mind and body are not regarded as a real dualism, but are different sides of one reality. They are separated in the form of sensation and stimulus; that is, what appears from a subjective viewpoint as the mind, appears from an external or objective viewpoint as the body. In the expression of the equation of Fechner's law (sensation intensity = C log stimulus intensity), it becomes evident that the dualism is not real. While this law has been criticized as illogical, and for not having universal applicability, it has been useful in research on hearing and vision.

Fechner's most significant contribution was made in his Elemente der Psychophysik (1860), a text of the "exact science of the functional relations, or relations of dependency, between body and mind," and in his Revision der Hauptpunkte der Psychophysik (1882). Upon these works mainly rests Fechner's fame as a psychologist, for in them he conceived, developed, and established new methods of mental measurement, and hence the beginning of quantitative experimental psychology. The three methods of measurement were the method of just-noticeable differences, the method of constant stimuli, and the method of average error. According to the authorities, the method of constant stimuli, called also the method of right and wrong cases, has become the most important of the three methods. It was further developed by G. E. Müller and F. M. Urban.

William James, who did not care for quantitative analysis or the statistical approach in psychology, dismisses the psychophysic law as an "idol of the den," the psychological outcome of which is nothing. However, the verdict of other appraisers is kinder, for they honor Fechner as the founder of experimental psychology.

Further Reading

• The major biographies of Fechner are in German. An account of him in English, with the original German bibliography, is in G. Stanley Hall, Founders of Modern Psychology (1912). For a treatment of Fechner's works and thought see T. Ribot, German Psychology of Today: The Empirical School (trans. 1886). For his philosophy see O. Klemm, History of Psychology (1911; trans. 1914), and George Sidney Brett, History of Psychology, vol. 3 (1921).