Pronuncia napoletana e pronuncia fiorentina

Why do Florentines say maèstro, dimòra, while Romans and Neapolitans say maéstro and dimóra. And why do Neapolitans say gésso, nódo, while Romans and Florentines say gèsso and nòdo? In the wake of a famous booklet by Bruno Migliorini, the present paper aims to describe and to explain the different incidence of mid vowels in the lexicon of Florentine, Roman and Neapolitan Italian. To this end, we shall invoke the role of substratum, phonetic analogy and the phantom of the lingua cortigiana.