He was born at Groß-Särchen, near Muskau, in Lower Lusatia, where his father was pastor. He was educated at Sorau and Dresden and at the University of Leipzig, the city in which he spent the rest of his life. In 1834 he was appointed professor of physics, but in 1839 contracted an eye disorder while studying the phenomena of color and vision, and, after much suffering, resigned. Subsequently recovering, he turned to the study of the mind and its relations with the body, giving public lectures on the subjects dealt with in his books.
Fechner's epoch-making work was his Elemente der Psychophysik (1860). He starts from the monistic thought that bodily facts and conscious facts, though not reducible one to the other, are different sides of one reality. His originality lies in trying to discover an exact mathematical relation between them. The most famous outcome of his inquiries is the law known as the Weber–Fechner law which may be expressed as follows:
Though holding good within certain limits only, the law has been found to be immensely useful. Fechner's law implies that sensation is a logarithmic function of physical intensity, which is impossible due to the logarithm's singularity at zero; therefore, S. S. Stevens proposed the more mathematically plausible power-law relation of sensation to intensity in his famous paper entitled "To Honor Fechner and Repeal His Law."
Fechner's general formula for getting at the number of units in any sensation is S = c log R, where S stands for the sensation, R for the stimulus numerically estimated, and c for a constant that must be separately determined by experiment in each particular order of sensibility. Fechner's reasoning has been criticized on the grounds that although stimuli are composite, sensations are not. "Every sensation," says William James, "presents itself as an indivisible unit; and it is quite impossible to read any clear meaning into the notion that they are masses of units combined."
He also studied the still-mysterious perceptual illusion of Fechner color, whereby colors are seen in a moving pattern of black and white.
Though he had a vast influence on psychophysics, the disciples of his general philosophy were few. Among them, however, was William James, who, in 1904, wrote an admiring introduction to the English translation of Fechner's Büchlein vom Leben nach dem Tode (Little Book of Life After Death). Fechner's world concept was highly animistic. He felt the thrill of life everywhere, in plants, earth, stars, the total universe. Man stands midway between the souls of plants and the souls of stars, who are angels. God, the soul of the universe, must be conceived as having an existence analogous to men. Natural laws are just the modes of the unfolding of God's perfection. In his last work Fechner, aged but full of hope, contrasts this joyous "daylight view" of the world with the dead, dreary "night view" of materialism. Fechner's work in aesthetics is also important. He conducted experiments to show that certain abstract forms and proportions are naturally pleasing to our senses, and gave some new illustrations of the working of aesthetic association.
Fechner's position in reference to predecessors and contemporaries is not very sharply defined. He was remotely a disciple of Schelling, learnt much from Benedict de Spinoza, Gottfried Wilhelm Leibniz, Johann Friedrich Herbart, Arthur Schopenhauer, and Christian Hermann Weisse, and decidedly rejected Georg Hegel and the monadism of Rudolf Hermann Lotze.
The standard intellectual biography of Fechner and his work in English is