"Qu'est-ce que la tonalité?" is the question raised by François-Joseph Fétis (1784-1871), a highly influential Belgian music theorist in the 19th century, in the several his theoretical works. As an answer the question, he defined "La tonalité se forme de la collection des rapports nécessaires, successifs ou simultanés, des sons de la gamme". He systematized diverse elements of harmony and rhythm under this concept of tonalité. Further to this, he was harshly critical of the major theories of tonality and harmony claimed by his predecessors and contemporary thinkers.
This brief study is focusing on the different explanations of the seventh chord on leading-tone, claimed by Fétis and Charles-Simon Catel (1773-1830) through analysis of Fétis' own arguments in his Traité complet de la théorie et de la pratique de l'harmonie. This analysis reveals that Fétis explained the process of chord generation consistently in relation to a major or minor scale, while Catel regarded chord as mere aggregation of tones independent of scale. Fetis' arguments seem to suggest the differences not only between their explanations about the chord generation, but also between their concepts of tonality itself.