Most Artes grammaticae of late antiquity start with a 'phonetic complex' traditionally placed into chapters entitled De voce and De lit(t)eris. The content and terminology of the complex became an object of criticism among humanist scholars. In this paper, the complex will be briefly characterized and then the attitude of Julius Caesar Scaliger towards the term lit(t)era in De causis linguae Latinae will be presented. This contribution will describe in detail Petrus Ramus's definitions of the key terms of the complex and his classification of Latin speech sounds based on a dichotomic approach. In the context of Ramus's dichotomic model of the Latin sound inventory, two vernacular models of the sound inventory of a Slavic language will be analysed. The aim of the paper is to outline how Ramus's approach was adopted in the grammatical texts of a Slavic language: Nudožerinus's Grammaticae Bohemicae libri duo and Anonymous's De litteratura Slavorum germanissima. This research was inspired by the statement of G. A. Padley in Trends in Vernacular Grammar I concerning the small degree of mutual awareness among scholars working in the Latin and vernacular grammatical traditions.