How did Christoph Willibald Gluck reduce the use of da capo arias?

Christoph Willibald Gluck sought to reform opera by prioritizing drama and "beautiful simplicity" over the rigid conventions of the era. He and his collaborators, particularly Ranieri Calzabigi, argued that the "true office" of music was to serve poetry, a goal they believed was hindered by the "useless and superfluous ornaments" found in florid da capo arias.1

Gluck reduced the use of da capo arias by protesting against several of their inherent dramatic flaws:2

• Dramatic Impropriety: He objected to the structural requirement of returning to the initial mood of the "A" section after the contrasting emotional development of the "B" section.2
• Excessive Ornamentation: He criticized the use of excessive coloratura, which he felt impeded the action and naturalness of expression.12
• Textual Absurdity: He opposed the repetition of text that often resulted from the da capo form, which he felt undermined the opera's function as a coherent drama.12

By moving away from these stereotypes, Gluck’s works were among the first to utilize a wider variety of aria forms, ranging from simple strophic songs to elaborate, dramatically integrated scenes.2