 William Heytesbury (c. 1313–1372/3), a member of Oxford’s Merton College and the School of “Oxford Calculators”, was most likely a student of Richard Kilvington, who was a younger contemporary of John Dumbleton. Heytesbury developed the works of Thomas Bradwardine and Richard Kilvington, and he was also influenced by Walter Burley, William Ockham, and Roger Swyneshed (or Swineshead). He authored a popular textbook Regulae solvendi sophismata and several other collections of sophisms. He linked interests in logic, mathematics, and physics. He formulated the Middle Degree Theorem (also known as the Mean Speed Theorem) offering a proper rule for uniformly accelerated motion, later developed by Galileo. His works anticipated nineteenth-century mathematical analyses of the continuum. He influenced logic in Britain and Italy (where several late fourteenth and early fifteenth-century editions of his texts were printed) and his influence lasted until the sixteenth century, when the debates he participated in declined.