William Heytesbury, a fellow at Merton College in Oxford from 1330, belonged to the second generation of Mertonian "Calculators." His work depends on Richard Kilvington's Sophismata (1325) and Thomas Bradwardine's Insolubilia and Tractatus de Proportionibus (1328). His technique was to analyze sophismata—ambiguous problematic statements whose truth or falsehood is to be assessed under specified assumptions—and apply supposition theory, a form of semantic-logical analysis, to the explication of their underlying logical grammar. He is particularly noted for his work on motion and the continuum.

Heytesbury's most popular work was the Rules for Solving Sophismata (1335), which contains six treatises: "On Insoluble Sentences (Insolubilia)," dealing with self-referential paradoxes; "On Knowing and Doubting," concerning reference in intensional contexts; "On Relative Terms," considering the reference of relative pronouns; "On Beginning and Ceasing" and "On Maxima and Minima," about continua; and "On the Three Categories," on velocity and acceleration...