Charles Sanders Peirce (1839-1914), American philosopher and physicist, born in Cambridge, Massachusetts, and educated at Harvard University. In 1861 Peirce was appointed to the U.S. Coast Survey. Between 1864 and 1884 he lectured intermittently on logic and philosophy at Johns Hopkins and Harvard universities, and in 1877 he became the first American representative to the International Geodetic Congress.

In 1861 Peirce began a series of experiments with pendulums that contributed greatly to the determination of the density and shape of the earth, and also an investigation of the measurement of light waves. In 1867 he turned his attention to the system of logic created by the British logician and mathematician George Boole, and he worked on extending and transforming Boolean algebra until 1885.

Peirce is best known for his philosophical system, later called pragmatism. According to his pragmatic philosophy, no object or concept possesses inherent validity or importance. Its significance lies only in the practical effects resulting from its use or application. The “truth” of an idea or object, therefore, can be measured by empirical investigation of its usefulness. The concept was expanded by the American philosophers William James and John Dewey, and it profoundly influenced modern philosophical and sociological thought. Peirce's works include Photometric Researches (1878) and Studies in Logic (1883). His essays appear in Chance, Love, and Logic, published posthumously in 1923.