Progression. Because Stravinsky makes use of the perfect fifth as a stable, referential structural unit in this music, as in so much of his earlier music, it becomes possible to think about large-scale harmonic motion in terms of the intervallic relationships among the structural fifths (which are heard sometimes as fourths, and sometimes as frames for melodic activity). The fourth block ends with reference to the perfect fifth, A♯-E♯. As the fifth block begins, the A♯ is sustained in the bass, moving down two semitones to G♯, just as the melody ascends to D♯, supported by G♯. That motion of structural perfect fifths, down two semitones from A♯-E♯ to G♯-D♯, can be related back to the first block, which ended with reference to F♯-C♯. The concluding G♯-D♯ can be thought of as the central, convergence point for F♯-C♯ below it and A♯-E♯ above it.