In the second half of the 15th century, Johannes Tinctoris distinguished two types of counterpoint: simplex and diminutus; the latter refers to the diminution of the value of the notes of simple counterpoint and also to the use of dissonances. At the turn of the 17th century, the controversy between Giovanni Maria Artusi and Claudio Monteverdi establishes a distinction between a prima pratica and a seconda pratica determined by a freer treatment of dissonances caused by an expressive emancipation. The aim of the thesis is to show how the theorists of the time reacted to the changes in music and to question the idea of a purely conservative theory by showing that there is also a first and a second phase in theory. The thesis will therefore highlight the transition between prima pratica and seconda pratica, especially in the works of Pietro Pontio and Artusi, to study in detail the treatment of dissonance from a technical point of view and to report and compare examples taken both from the treatises themselves and from the contemporary repertoire.