In Fig. 4, we have a progression of Im–VI–IVm–VII in C minor played under a riff that first alternates between Cm and Csus2 chords, and then between Bb and Bbsus2 chords.

Predictably, the first and fourth measures of the rhythm part assume the character of the chords outlined by the lead riff. But some pretty neat stuff transpires on the Ab5 and F5. The notes C and G lift the Ab5 chord to make it into an Abmaj7. In the second half of the bar, the D adds to that a #11. Next, G and Eb, played over F5, suggest an Fm9 chord. When Eb in the riff scooches down a fret to D, we get the sense of an Fm6/9 chord. By the way, m6/9 is one of the coolest chords in all of music.

Fig. 5 features a riff playing two notes at a time. Each note, in turn, leads away from the tonal center by a half-step, and then back again as the progression cycles around. The root motion is I-bVII-IV-bVII and ends on I.

The D and G# in the lead riff combine with E5 to form an E7 chord. Then G# moves a half-step up to A so that at bVII, both rhythm and lead parts are playing a D5. Next, D slips down a fret to C# in the lead part, joining forces with an A5 to make an A major triad. Then it’s back to D5 before ending on E7.