Major Triad · Theory

Triad Minor Triad Major Scale Harmonic Function

A major triad in one line: a major third below, a minor third above.

C–E–G: C to E is a major third (4 semitones), E to G is a minor third (3)

It sounds stable for three verifiable reasons:

Reason	Explanation
It contains a perfect fifth	Root to fifth is 7 semitones, the most consonant interval after the octave
It contains a major third	Root to third is major, and partials 4, 5 and 6 of the harmonic series are exactly this shape (see [[concept:harmonic-series
It contains no semitone clash	The internal intervals are a major and a minor third — no minor second or tritone pulling for resolution

The third is the most tangible: spread the three notes out and there is nothing that demands immediate resolution. That is what "stable" means technically.

Where it appears

Every major scale contains three major triads: on degrees I, IV and V. Those three are the tonal skeleton (tonic, subdominant, dominant) and the harmonic backbone of nearly all classical music (see harmonic function).

Natural minor has fewer, but not none: degrees III, VI and VII are major triads — which is a common source of those sudden brightenings in minor-key music.

The one difference from a minor triad

Lower the third by a semitone and you have a minor triad:

major: C–E–G　　 minor: C–E♭–G

One note, and stability and brightness both invert. It also shows that a chord's character rests mainly on its third, while the fifth supplies the frame.

Diagram: one note apart

Listen: the major triad

Common misconceptions

"A major triad is a happy chord." It supplies stability. Laments written in major triads are common.
"In a major key all the chords are major." Only three of the seven degrees (I, IV, V) are.
"A major third on the bottom makes a major triad." The upper third must be minor too. Two major thirds make an augmented triad.
"Inverting it stops it being a major triad." Quality is fixed by the notes; inversion changes only the bass.

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Listen in the library

Scales, Arpeggios, and CadencesC13:22Major-triad arpeggios in scale exercises — the three notes in turn, showing why the chord stands so firmlyDetailsSound Ye the Trumpet CallC10:35An organ hymn — block-voiced major triads, the commonest resting point in traditional harmonyDetails12 Variations on Ah vous dirai-je maman K.265/300eC17:31The Ah vous variations — the tonic triad is major, and the sense of stability comes from itDetails

All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).

Sources

大三和弦 = 大三度 + 小三度，根音到五音为纯五度，属和声学通则
大三和弦在主—属功能关系中的核心地位，为通行和声学表述

Used for fact-checking only; all prose is original.

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