Triads · Jazz Wiki

A triad is three notes stacked in thirds: root, third, fifth. It’s the smallest unit that can sound like a complete chord rather than just an interval, and every richer harmony in jazz — Seventh Chords, extended voicings, Upper Structure Triads — is a triad with something added on top. Learn the four triad qualities cold and you can read almost any chord symbol on a lead sheet at a glance.

Why stacking thirds works

Thirds sound stable because they sit close to the simple frequency ratios found in The Overtone Series — a major third and perfect fifth above a root are ringing out overtones of that root, more or less. This is why stacked-third chords (Tertian Harmony) became the default building block of Western harmony, as opposed to stacking fourths (Quartal Harmony), which gives a more open, ambiguous sound. Two Intervals of a third on top of each other — a root-third and a third-fifth — is all it takes to define a triad’s quality, because the size of each third (major or minor) determines whether the chord sounds bright, dark, tense, or floating.

The four qualities, spelled out in C

Every triad quality comes from just two choices: is the bottom third major or minor, and is the top third major or minor. Only four combinations exist, and each has a completely different character:

Major — C–E–G (major 3rd + minor 3rd, root to fifth = perfect 5th)
Minor — C–E♭–G (minor 3rd + major 3rd, root to fifth = perfect 5th)
Diminished — C–E♭–G♭ (minor 3rd + minor 3rd, root to fifth = diminished 5th)
Augmented — C–E–G♯ (major 3rd + major 3rd, root to fifth = augmented 5th)

Major triad: major third on the bottom

A major third under a minor third — the perfect fifth between root and top anchors the bright, stable major sound

Minor triad: the two thirds swapped

E♭b3

Flip the order — minor third under major third — and the chord turns dark; the other two combinations give diminished (m3+m3) and augmented (M3+M3)

Here are all four qualities built on C:

Major and minor sound stable and consonant (Consonance and Dissonance) because the perfect fifth anchors them. Diminished and augmented are inherently less stable: the diminished triad’s flatted fifth wants to resolve inward, and the augmented triad is symmetrical — divide the octave into three equal major thirds and you get the same shape no matter which note you call the root, so it has no built-in pull toward any single tonic.

The seven triads hiding inside every major scale

Take The Major Scale and build a triad on each degree using only the notes already in that scale, and you get a fixed, memorizable pattern of qualities. This is Diatonic Harmony in its rawest form, and it’s usually labeled with Roman Numeral Analysis so it transfers to any key:

Degree	Roman numeral	C major	Quality
1	I	C (C–E–G)	Major
2	ii	Dm (D–F–A)	Minor
3	iii	Em (E–G–B)	Minor
4	IV	F (F–A–C)	Major
5	V	G (G–B–D)	Major
6	vi	Am (A–C–E)	Minor
7	vii°	B° (B–D–F)	Diminished

Here are all seven diatonic triads in C major, root position:

That pattern — major, minor, minor, major, major, minor, diminished — is identical in every major key. It’s worth internalizing rather than deriving each time, because it’s the map you’ll use constantly to figure out what a ii or a V “should” be before any alterations get added.

Where triads go once you start stacking more

A triad rarely stays a bare three-note chord for long. Stack another third on top and you get a seventh chord — Cmaj7 is just a C major triad plus a major seventh, Cm7 is a C minor triad plus a minor seventh, and a half-diminished chord is a diminished triad plus a minor seventh. Reorder the three notes so the third or fifth is on the bottom and you’ve made a chord inversion — same triad, same quality, different note in the bass, often written as a slash chord like C/E. And in more modern jazz, triads get treated as movable objects in their own right: an upper-structure triad is a major or minor triad borrowed from outside the underlying chord and laid on top of it to color a dominant chord, while triad pairs use two triads a step or a tritone apart as a scale substitute for improvising. Even the Diminished Seventh Chord, which sounds far more exotic than a plain triad, is built by simply continuing the diminished triad’s stack of minor thirds one note further.

♫ Listen

Bill Evans Trio — “Autumn Leaves” (Portrait in Jazz, 1960): through the opening choruses, notice how Evans’s left-hand voicings often set a simple triad shape above the bass note rather than spelling full root-position chords — the triad’s color floats free of the root.
John Coltrane — “My Favorite Things” (My Favorite Things, 1961): in the long piano vamp and his solo, McCoy Tyner stacks simple triadic shapes into open, ringing voicings that outline the modal harmony without dense extensions.