Tertian Harmony · Jazz Wiki

Tertian harmony is the system of building chords by stacking thirds on top of a root — third on third on third, straight up. It is the default harmonic language of jazz and Western tonal music because it is the most consonant, stable way to pile up notes, and it gives every chord a clear root, a clear quality, and a clear place to resolve to. Almost every chord symbol you will ever read in a fake book — from a plain triad to a Cmaj13#11 — is a tertian stack dressed up with more or fewer floors.

Why thirds build stable chords

Stack a major third and a minor third on C and you get C–E–G, a major triad — and that shape isn’t arbitrary. The first three distinct pitches of the overtone series above C are C, G, and E, so a major triad is literally the shape the harmonic series wants to make. That acoustic grounding is why tertian chords sound so settled compared to stacks of fourths or seconds, and it’s the reason consonance in tonal music is measured against the major triad as the baseline.

Keep stacking thirds and you get the whole vocabulary of jazz harmony in order:

Root + 3rd + 5th = triad (3 notes)
- 7th = seventh chord (4 notes)
- 9th, 11th, 13th = extensions (chord tones repeating an octave up)

Spelling it out in real keys

Here’s the same tertian stack — root, third, fifth, seventh — spelled in four common keys:

C: C–E–G–B (Cmaj7)
F: F–A–C–E (Fmaj7)
B♭: B♭–D–F–A♭ (B♭7, dominant)
E♭: E♭–G–B♭–D (E♭maj7)

Here are those four stacks notated as sounding chords:

Extending a dominant chord just continues the same third-stacking logic past the seventh:

C7 = C–E–G–B♭ (root, maj3, perf5, min7)
C9 = C–E–G–B♭–D (add the 9th, a third above the 7th)
C13 = C–E–G–B♭–D–F–A (the full stack through the 13th)

C13: one tertian stack, floor by floor

A13

F11

extensions above the seventh

B♭b7

The first three floors are the triad, the fourth makes it a seventh chord, and every third stacked past the b7 is an extension — the same third-on-third logic all the way up

In practice nobody plays all seven notes of a C13 — pianists and guitarists pick the chord tones that matter (usually the 3rd, 7th, and the extension that gives the chord its color) and let the bass or another instrument imply the root. That selective approach is what voicing is about, and it’s how tertian theory turns into something playable.

From triads to functional harmony

Because every tertian chord has a built-in “next third” to resolve toward or away from, tertian stacks are what make diatonic harmony and functional progressions work in the first place. A ii–V–I in B♭ is nothing but three tertian seventh chords in a row, each one a stack of thirds over its own root:

Cm7 – F7 – B♭maj7

The seventh of F7 (E♭) wants to fall to the third of B♭maj7 (D) — that half-step pull exists because tertian chords share so many close notes between changes, which is also the engine behind smooth voice leading. Chord symbols themselves are basically shorthand for “here’s which thirds are stacked and where.”

Where the stack stops working

Tertian harmony isn’t the only option, and by the late 1950s players started leaning on its opposite. Quartal harmony stacks fourths instead of thirds, producing open, ambiguous sonorities that don’t demand resolution the way tertian chords do — you hear this shift explicitly in modal jazz, where a static scale, not a chain of resolving tertian chords, is the point. Even inside otherwise tertian tunes, players started borrowing quartal-flavored color via upper structure triads and quartal voicings layered over a tertian bass — proof that the two systems aren’t enemies so much as two different tools for two different sounds.

♫ Listen

Bill Evans Trio — “Autumn Leaves” (Portrait in Jazz, 1959): Evans’s comping through the ii–V–I changes (Cm7–F7–B♭maj7 and its relatives) is tertian harmony at its most refined — listen to how little each voice moves from chord to chord, especially into the bridge.
Miles Davis — “So What” (Kind of Blue, 1959): the famous opening voicing under Paul Chambers’s bass statement is Evans stacking a tertian Dm7 in fourths-and-thirds hybrid spacing — a good place to hear tertian chord tones dressed in an almost-quartal voicing, right before the tune settles into pure modal territory.