Major triad

Structure

The major triad is a root with two stacked thirds: at the bottom the major third (4 semitones), above it the minor third (3 semitones). The outer fifth is perfect and gives a stable, resting sound. The sound is bright, open, often cheerful, but that is a rule of thumb, not a rule.

Physically the major triad is already laid down in every single note: the major third has the ratio 5:4 and is the fifth partial in the harmonic series of any note. Minor does not occur in a comparable place there. That does not explain, however, why we hear minor as sad.

Major triads in a key

In a major key the degrees I, IV and V carry major triads: in C major C, F and G, the three main functions tonic, subdominant and dominant. In natural minor the degrees III, VI and VII also carry major triads (in A minor C, F and G); with the raised seventh degree V becomes a major triad too (E major). A minor piece that ends on a major triad uses the Picardy third. In chord symbols the major triad appears as the bare letter: C.

Common mistakes

• Swapping the thirds: In the major triad the major third lies at the bottom, in minor the minor third.
• Forgetting the third: Without the third, the chord has no major or minor colour.
• Doubling the third: In four-part writing you double the root, if need be the fifth.