Figure 7.3.8. (a) The “down a third, up a step” sequence can be derived from more familiar sequences by exchanging root position and first-inversion chords. Here, the four forms on the bottom staff, are derived from the descending-fifth and descending-step sequences in the upper staff. (b) Measures 62-66 from Contrapunctus X in Bach’s Art of the Fugue. Here, root substitution over a fixed bass line changes the descending fifths progression into the “down a third, up a step” progression.