Why do Antonio Vivaldi’s slow concerto movements resemble vocal arias?

Antonio Vivaldi’s slow concerto movements often resemble vocal arias because they frequently employ an ostinato—a simple, freely recurring bass line—that serves as a foundation for the solo instrument.1

In these movements, the bass line provides a steady, repetitive structure while the solo instrument enters, often on long tones, and gradually unfolds into decorative, expressive passages. When the recurrences of the ostinato are sufficiently free and the bass and treble melodies are distinct, the resulting texture creates the effect of an expressive aria with a clear prelude and postlude. This approach reflects the broader influence of operatic styles on the Baroque concerto, where instrumental music adopted the lyricism and dramatic character of vocal works.12