Mozart’s Piano Sonata in C major, K.545 is often called a textbook of Classical harmony,

 Mozart’s Piano Sonata in C major, K.545 is often called a textbook of Classical harmony, especially in the first movement where the cadential formula ii → I⁶⁴ (cadential 6-4) → V → I appears in the closing section. In Classical practice, the ii chord functions as a “predominant,” leading into the dominant, and thereby strengthening the V–I resolution. Thus, the ii–V–I exists in Classical music, but unlike in jazz, it is not repeated cyclically; rather, it appears as a standard device to establish closure. By contrast, in jazz standards such as Autumn Leaves, the ii–V–I progression forms the backbone of the piece, continuously unfolding with added tensions and substitutions to enrich the sonority. Conversely, jazz also features progressions close to the Classical I–IV–V–I, as in C Jam Blues or When the Saints Go Marching In, where the simple triadic movement between I, IV, and V is foundational. Yet, in performance, these are quickly expanded with tensions, substitutions, or turnarounds. In essence, Classical harmony emphasizes the organization of tension and resolution, while jazz emphasizes the color and expansiveness of harmonic sound. The closing passage of K.545, with its ii–I⁶⁴–V–I cadence, can therefore be regarded as the closest Classical parallel to the “Autumn Leaves” type of progression.