After having recalled the positions of the theorists of tonal language, this work defines the principles which govern harmony in the classical period. The book describes the gradual enrichment of vocabulary and syntax during the Romantic century. Finally, he examines the delicate question of the weakening of the tonality as the twentieth century approaches. An essential synthesis, with many examples taken from the works of Haydn to Debussy, including those of Mozart, Schumann, Liszt, Wagner, …