The harmonic structure of the rhapsody is more difficult to analyze. The piece begins and ends in B major, but it modulates towards the sub-dominant direction and abruptly returns to B major at the end. The opening modulates "downward" through the keys B, E, A, D, G, B, E, and finally to A major. Modulation through the circle of fifths in the reverse direction inverts classical tonal relationships, but does not abandon them. The entire middle section resides primarily in C major, with forays into G major (the dominant relation). Such modulations occur freely, although not always with harmonic direction. Gershwin frequently uses a recursive harmonic progression of minor thirds to give the illusion of motion when in fact a passage does not change key from beginning to end. Modulation by thirds is a common feature of Tin Pan Alley music.
The harmonic structure of the rhapsody is more difficult to analyze. The piece begins and ends in B major, but it modulates towards the sub-dominant direction and abruptly returns to B major at the end. The opening modulates "downward" through the keys B, E, A, D, G, B, E, and finally to A major. Modulation through the circle of fifths in the reverse direction inverts classical tonal relationships, but does not abandon them. The entire middle section resides primarily in C major, with forays into G major (the dominant relation). Such modulations occur freely although not always with harmonic direction. Gershwin frequently uses a recursive harmonic progression of minor thirds to give the illusion of motion when in fact a passage does not change key from beginning to end. Modulation by thirds is a common feature of Tin Pan Alley music.