French Scholastic philosopher and a leading member of the School of Chartres.

A pupil of the philosopher Bernard of Chartres, he taught at Chartres and Paris and was tutor to Henry (later Henry II of England), son of Geoffrey Plantagenet.

William, a realist whose ideas leaned toward pantheism, gave an atomistic explanation of nature, the four elements (air, water, fire, earth) being regarded as combinations of homogeneous individual atoms. He wrote explanations of Plato's Timaeus and Boethius' De consolatione philosophiae (“The Consolation of Philosophy”), and composed two original works, Philosophia Mundi (“Philosophy of the World”) and Pragmaticon Philosophiae (“The Business of Philosophy”). He is also considered to be the author of the Summa Moralium Philosophorum (“The Substance of the Ethical Philosophies”), the earliest medieval treatise on ethics.