Triad
A triad is the chord of root, third and fifth. It arises when you stack two thirds on top of each other and is the basic building block of harmony. There are four kinds: major, minor, diminished and augmented.
Stacking thirds
You start with a root and skip every other note of the scale. From C this gives C–E–G, the C major triad. The three tones are called root, third and fifth. Whether the triad sounds bright or dark is decided by the lower third, measured in semitone steps.
| Triad | Thirds bottom + top | Fifth | Example on C |
|---|---|---|---|
| major | major + minor 4 + 3 semitones | perfect | C C–E–G |
| minor | minor + major 3 + 4 semitones | perfect | Cm C–E♭–G |
| diminished | minor + minor 3 + 3 semitones | diminished | C° C–E♭–G♭ |
| augmented | major + major 4 + 4 semitones | augmented | C+ C–E–G♯ |
In major and minor the outer fifth is perfect (7 semitones) and gives a stable, restful sound. Diminished and augmented triads sound unstable because their fifth is narrowed or widened. They ask for resolution. The diminished triad has a tense, restless sound, the augmented one a floating, hard-to-place one.
Triads in a key
If you build a triad on every degree of a major scale using only notes of the scale, seven chords arise. In C major they are C, Dm, Em, F, G, Am and B°. Capital Roman numerals stand for major, lowercase ones for minor, the degree sign for diminished. A triad does not change its name when the root is not at the bottom: then we speak of inversions, as explained on the page Chords.
Common mistakes
- Counting only the fifth: The third decides between major and minor.
- Mixing up diminished and augmented triads: Diminished has two minor thirds, augmented two major ones.
- Mixing up triad and seventh chord: A triad has three tones, a seventh chord four.
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Related terms
ChordMajor triadMinor triadSeventh chordChord inversionRootThirdDiatonic chordDiminishedAugmented
Editor: Maik Krohm · reviewed on 3 October 2026
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