Which movement type is commonly found in a sonata, functioning within a ternary form?

In the context of sonatas, the movement type that commonly functions within a ternary form is often Adagio. This is because many sonatas typically contain a slow movement that is reflective and lyrical, aligning with the characteristics of Adagio, which indicates a slow tempo. Ternary form, which is structured as A-B-A, suits this type of movement well, allowing for contrasting themes while providing a return to the primary material.

Adagio movements serve as the emotional core of a sonata, contrasting with faster movements that often carry more energy and technical demands. While Allegro and Vivace represent faster tempos and energetic qualities that are frequently found in the outer movements of sonatas, they do not typically align with the lyrical and expressively slow nature that an Adagio movement offers. Largo, although also slow, is less commonly designated to this specific structural role. Thus, Adagio effectively embodies the traits needed in a ternary form within a sonata.