WILLIAM OF HEYTESBURY

Scholastic, logician, chancellor of the University of Oxford (also known as Hentisbury, Hesberi, Tisbery); b. most likely in Wiltshire, England, c. 1313; d. December 1372, or January 1373. He became a fellow of Merton College, Oxford, by 1330, when thomas bradwardine, Simon Bredon, and thomas of buckingham were already members. Merton had been founded by Bp. walter of merton primarily as a residence for theological students, although young masters in arts were allowed to complete their regency before enrolling in the faculty of theology. By February 1340, Heytesbury was already a student of theology, for he was named one of the foundation fellows of Queen's College, which was restricted to theological students. He returned shortly to Merton, where he remained at least until 1348, and where he was ordained, April 15, 1346. By July 1348, he was a "doctor in theology," but the date of his inception is unknown. He retained numerous benefices until his death, among them the rectorship of St. John's in Ickham, Kent (1354). In a university roll for papal graces, compiled before February 1363, Heytesbury is called "late Chancellor of the University." If this title is correct, he must have held office from 1353 to 1354, the only period for which no chancellor is known, or else he merely served temporarily between two chancellorships. According to another document, he was again chancellor on Nov. 9, 1371; hence the conjecture that Heytesbury held office from Pentecost 1370 until Pentecost 1372.

Heytesbury accepted the fundamental ideas of william of ockham, particularly on logical supposition, substance, quantity, motion, and time. He also favored the new kinematic theorem of Thomas Bradwardine and attempted to apply it to the intension and remission of all qualitative forms, including knowledge and doubt. His works in logic, probably written between 1331 and 1339, were popular aids to young "sophisters" in the university for responses and determination; and his beginners' text, Natural Terms (Termini naturales ), contained the standard definitions needed in natural philosophy. His widely used Logic, or Rules for Solving Sophismata (Regulae solvendi sophismata ), "given at Oxford in 1335," was addressed to first–year students of logic; the equivocal terms involved include various types of motion, knowing and doubting, beginning and ceasing, maximum and minimum, and relatives. The Proofs of Conclusions (Probationes conclusionum ), attributed to him, involves the same equivocal terms and contains the first known proof of the theorem of mean speed. These works, together with his Sophismata XXXII, De sensu composito et diviso, and a famous Treatise on Consequences, served as textbooks in the universities of Vienna, Erfurt, Padua, and other continental schools as late as the 16th century. Nothing is known of his theological views.

Bibliography: p. m. m. duhem, Études sur Léonard de Vinci, 3 v. (Paris 1955) 3:405–409, 493–510. g. sarton, Introduction to the History of Science, 3 v. in 5 (Baltimore 1927–48) 3.1:565–566. c. wilson, William Heytesbury: Medieval Logic and the Rise of Mathematical Physics (Madison, Wis. 1956). a. b. emden, A Biographical Register of the Universtiy of Oxford to A. D. 1500, 3 v. (Oxford 1957–59) 2:927–928. m. clagett, Science of Mechanics in the Middle Ages (Madison, Wis. 1959) 235–242; 263–289 and passim.

[j. a. weisheipl]