c. Given this definition, historical continuity can be established in a direct line from Mozart to Verdi and Wagner.
Verdi's career began at a time when Italian opera was dominated by the bel-canto tradition, in which, the singer was considered the central element. The soprano (or, a bit earlier, the castrato), after the inevitable four-bar introduction, would stop the recitativo action of the narrative, step forward thus announced and sing, using all her coloratura, a tuneful set piece which showed off her virtuosity using rigidly standardized vocal conventions which were generally composed for (if not totally controlled by) that purpose, generally with little or no contextual significance. She would often be recalled for an encore leaving the stage and returning for ovation after ovation while the other principals stood woodenly around waiting for the resumption of the drama, like a game of "Statutes." The music composed for her solo may have fallen anywhere in a range of emotions or of beauty. (Certainly, both Bellini and Donizetti wrote lovely arioso passages.) Yet, in the same way that the spoken drama in the modern musical is artificially and jarringly interrupted by the set-piece song (ask any child who has just seen "South Pacific"), the bel-canto conventions were anti-dramatic.
There were important contributions made in attempting to alter the situation of the parallel drama and music, to interrupt the tradition of interrupting the action: Rossini emphasized the declamatory nature of the aria and recitative both and symphonized the opera orchestra; Donizetto dramatized and tragedized the libretto; Bellini left a legacy of beautiful melody, as distinct from beautiful embellishments; but it was Verdi who slowly, over a long career, "operatized" the form. As Ralph Vaughan Williams put it:
Verdi wrote operas. He did not add music to plays
full of superficial philosophy or bogus psychology
. . . it ...