Take Ex. 1, for instance. As well as being the mother of all Delta blues turnarounds—embraced by guitarists from Robert Johnson to Billy Gibbons—it’s an excellent example of oblique motion, one of the three types of movement we can create using two layered lines. Notice how the top voice
(A, on the first string) stays constant, while the lower voice (G, F#, Fn, E) descends chromatically on the fourth string. Oblique motion occurs when one voice remains stationary as the other rises or falls against it—exactly what’s happening in this example. In the process of layering these two lines, we imply four chords—A7, D, Dm, and A.
Ex. 2 illustrates parallel motion, in which two voices move up or down while locked to the identical interval. Jimi Hendrix and Eric Johnson are among the greats who rely on parallel motion to generate droney textures. In this example, we move a line on the fourth string accompanied by a second-string line that’s a perfect fifth higher. This two-string grip slides gracefully along the fretboard, making it ideal for ringing riffage.
When two layered lines move in opposite directions, they produce contrary motion, as shown in Ex. 3. Here the top line (D, E, F#, G, A) ascends on the second and first strings, while the bottom line
(D, C, B, B, A) descends on the fourth and fifth. As in our previous examples, the two lines suggest a chord progression, in this case, D, C, Bm, Gm/B, and A.
The fun begins when you combine contrary, parallel, and oblique motion to forge cool guitar parts, as we’ll discover in the next few lessons.