ABSTRACT
The tonic is prolonged in mm. 1-4 and then morphed into a V7/IV in m. 5. The tonic prolongation takes the form of an idiomatic Imaj7-vi7-ii7-V7 progression, which lends itself to a variety of harmonic substitutions. The subdominant controls mm. 5-6 and is capable of many surface realizations. Next, mm. 7-8 proceed to the dominant, which can also be idiomatically expanded, transformed, and/or confirmed. The A section of rhythm changes is also known as an eight-bar blues because it contains the harmonic paradigm of the blues: tonic in m. 1, subdominant in m. 6, and dominant in m. 8.4 This foreshortened blues preserves the structural weight of the fundamental chords, as the tonic controls the longest span (mm. 1-4), the subdominant occupies the shorter span (mm. 6-7), and the dominant (m. 8) becomes subject to various harmonic modifications.
