This paper argues that the 14th-century Oxford Carmelite Richard Lavenham was the author of the treatise De syncategorematibus that was used as a textbook in 15th-century Cambridge, a version of which was printed several times in the late 15th and early 16th centuries in the Libellus sophistarum ad usum Cantabrigiensium. The manuscript versions of this treatise differ significantly from one another and from the printed editions, so that the claim of Lavenham’s authorship needs to be carefully considered. The evidence for this claim is described briefly. The identification of the De syncategorematibus in the Cambridge Libellus as Lavenham’s provides the first real indication that Lavenham, whose works testify to the influence of other authors on logico-linguistic studies in late 14th-century Oxford, was himself not without influence as late as the early 16th century. On the other hand, the De syncategorematibus is not a very competent treatise, so that its inclusion as a textbook in the Libellus sophistarum is an indication of the decline of the logical study of language in England during this period. A brief analysis of the contents of the treatise supports this observation.