Parallel Motion and Planing

Planing is what happens when you stop asking “where does this chord want to go” and start asking “what does this shape sound like slid up or down.” You take a voicing, keep its exact intervallic skeleton, and drag it through a scale or a chromatic line. The result is harmony as color and texture rather than function — motion you feel in your ear, not motion that resolves.

Why parallel fifths stopped being a crime

Common-practice Voice Leading bans parallel fifths and octaves because they collapse the independence of voices — two lines moving in lockstep stop sounding like two lines. Debussy, writing around the 1890s–1900s, treated that same collapse as a feature: if voices move together, the chord becomes one thick, glowing object you can push around like a single color. A Paris Conservatory professor reportedly called his parallel chords “theoretically absurd,” which is exactly the point — planing is a deliberate rejection of functional constraint in favor of atmosphere. Jazz inherited this permission and ran with it, especially once Modal Jazz needed harmony that could float over a static center instead of driving toward one.

Two ways to plane: diatonic and chromatic

There are really only two moves, and the difference is whether the chord quality is allowed to change.

Diatonic planing — the shape stays inside a key, so quality shifts with scale degree: Dm7 – Em7 – Fmaj7 – G7, the same four-note stack walked up the C major scale, landing as whatever chord type each degree produces.
Chromatic planing — accidentals preserve the exact same chord quality at every step: Dm7 – D♭m7 – Cm7, a pure m7 shape sliding by half-step, completely untethered from any key center.

The diatonic example above, walked as four-note stacks up the C major scale:

Diatonic planing sounds “inside” because it’s still borrowing the scale’s logic; chromatic planing sounds like it’s floating free, which is why it shows up as a color effect more than a harmonic argument.

Quartal stacks and the sound of modal jazz

The clearest laboratory for planing is Quartal Harmony — chords built from stacked fourths instead of thirds — because a fourths-stack has no clear functional identity to begin with, so sliding it around reads purely as texture. McCoy Tyner made this his signature: over a static F7sus4 vamp, his left hand plants a shape like F–B♭–E♭ and walks it up in parallel, generating a hypnotic, almost drone-like motion underneath the improvisation. Walking diatonic fourths straight up the C major scale gives you C–F–B, D–G–C, E–A–D, F–B–E — note that the stacks on C and F contain the augmented fourth F–B, which is the one wrinkle diatonic planing always introduces. Bill Evans used a related device, the five-note “So What” voicing (E–A–D–G–B — three stacked fourths topped by a major third), planing it down a whole step for the answering “amen” chords on “So What” as pure Comping color rather than functional accompaniment.

Tyner’s F–B♭–E♭ shape planed up in whole steps:

From locked hands to sus-chord planing

Planing doesn’t require Modal Harmony — it also lives in dense, orchestral piano textures. Milt Buckner’s 1940s “locked hands” technique, popularized by George Shearing as Four-Way Close Block Chords, moves a thick parallel chord shape in rhythmic lockstep with the melody, essentially planing the whole texture note-for-note. Herbie Hancock does something similar with Suspended Chords on “Maiden Voyage”: the A section slides one sus-chord shape between D7sus (often written Am7/D) and F7sus (Cm7/F), and the bridge keeps moving it to new roots, producing the tune’s signature drifting, oceanic feel. Related but distinct is Side-Slipping, which plans a single half-step or whole-step shift of one voicing rather than a sustained parallel run — a quick color jab instead of a current. Planing is also easy to confuse with Constant Structure: planing moves one shape vertically through a scale, while constant structure chains chords of the same quality across different, often unrelated roots — related family, different mechanism.

♫ Listen

Herbie Hancock — “Maiden Voyage” (Maiden Voyage, Blue Note, 1965): sus4 voicings plane diatonically under the head, creating the tune’s floating, tideless sense of harmony with no pull toward resolution.
McCoy Tyner — “Passion Dance” (The Real McCoy, Blue Note, 1967): stacked-fourth quartal shapes plane in the left hand under the F7sus vamp, generating a trance-like modal churn beneath the solos.
Bill Evans (piano) — “So What” (Kind of Blue, Miles Davis, Columbia, 1959): the five-note “So What” voicing answers the head’s opening phrase and reappears as planed comping color throughout the tune.