This is a study of the anonymous Destructions of the Modes of Signifying (DMS). Produced in the mid- to late fourteenth century and occasionally attributed to the famous French cardinal Peter of Ailly (1351–1420), the DMS is one of very few surviving texts representative of late medieval anti-modist polemics. A fundamental tenet of modism is what I call 'the Modist Correspondence Thesis' ('MCT'), which asserts that the syntactic features of language are grounded in the ontological properties of the world. The DMS argues forcefully against MCT and offers an alternative theory that grounds syntax in mental language. Part 1 of the dissertation is an essay addressing the issue of authorship. Part 2 is an essay focusing on MCT and the negative project of repudiating modism. Part 3 provides a Latin edition and English translation of the text of the DMS.