The study focuses on the descriptions of vowels in 18th century German textbooks on grammar, poetics and stylistics. The material are the works of J. Chr. Gottsched and J. Chr. Adelung, presenting two approaches to the qualification of German vowels in the same phonetic positions. The interpretation of the speech material taken from the works of the two German scientists is carried out by the methods of component, distributive and context-interpretative analysis. The observations of Gottsched and Adelung are considered against the background of the theoretical achievements of modern German and general phonetics. The study concerns rules for pronouncing vowels in the suffixes -bar, -haft, -heit, etc. Gottsched states them in terms of syllable length while Adelung uses tonal features (the presence or absence of main or secondary stress). The two descriptions reflect a phonetic phenomenon that is also characteristic of the modern German language - the complex nature of German stress, which combines musical, dynamic and quantitative components. The similarities and differences in the views of Gottsched and Adelung on the nature of stress in German are also studied by their works on stylistics and poetics. Gottsched interprets poetic meters as combinations of long and short syllables, without a reference to tone, while Adelung considers both syllable length and stress and establishes a dependency between them. The concepts of Gottsched and Adelung are not mutually exclusive: while Adelung's description is characterized by greater detail, the two scholars focus on different aspects of the same phonetic phenomena. Refs 16.