How did the Florentine dialect become the basis for standard Italian?

The Florentine dialect became the basis for standard Italian primarily through its adoption by preeminent literary figures and the subsequent efforts of linguistic institutions.

During the late 13th century, Tuscan—specifically the dialect of Florence—emerged as the primary vernacular in a peninsula otherwise defined by diverse regional dialects. The preeminence of this dialect was solidified by the works of three major writers: Dante Alighieri, whose The Divine Comedy demonstrated the power of the vernacular; Petrarch; and Giovanni Boccaccio.123

In the 16th and 17th centuries, the Crusca Academy was founded in Florence to refine and preserve the language. By treating the works of Petrarch and Boccaccio as models for linguistic usage, the academy established the Florentine dialect as the standard for Italian literature. Through these literary and academic channels, the Florentine variety evolved into the standard form of the Italian language used today.41