Why did Leon Battista Alberti write some of his works in the Tuscan vernacular?

Leon Battista Alberti wrote several of his moral and philosophical dialogues in the Tuscan vernacular to reach a broad urban audience that was not skilled in Latin, whom he referred to as the non litteratissimi cittadini.1

By using the vernacular, he aimed to provide this bourgeois society with the practical, reasonable counsel of the ancients regarding daily concerns such as family, friendship, education, and the common good. Furthermore, through works like his Regule lingue Florentine (the first Italian grammar), Alberti sought to demonstrate that the Tuscan vernacular was as regular and structured as Latin, thereby proving its worthiness for serious literary and intellectual use. This advocacy for the vernacular was a direct outgrowth of the evangelistic thrust of his humanism, which sought to make learning accessible and relevant to all experience.12