This article deals with Walter Burley’s (1275 – 1344) propositional semantics. Its aim is to examine his notion known as propositio in re (i.e. real proposition). All his relevant texts written between 1297 and 1337 are taken into account, first of all his commentaries on Aristotle’s Categories, On Interpretation and Posterior Analytics. This study is divided into three parts: in the first one an old controversy concerning the subject of logic is mentioned, as well as Burley’s own answer to it; the second part sheds light on Burley’s early articulation of his propositional theory; the final part focuses on the definitive explanation and justification of this theory from his last commentary on the Ars fetus from 1337.