The four qualities · Triads · Music theory
According to their intervals above the root there are four triads. The major triad has a major 3rd and a perfect 5th; the minor, a minor 3rd and a perfect…
The four qualities
According to their intervals above the root there are four triads. The major triad has a major 3rd and a perfect 5th; the minor, a minor 3rd and a perfect 5th; the diminished, a minor 3rd and a diminished 5th, and the augmented, a major 3rd and an augmented 5th.
Seen another way, the major triad is a major 3rd with a minor one on top and the minor triad, a minor 3rd with a major one on top; the diminished is two minor thirds and the augmented, two major ones. Major and minor triads are consonant; diminished and augmented, dissonant because of their 5th.
Building any triad
You only need to know how to build thirds. Write the three letter names skipping one each time (C–E–G, F–A–C, B–D–F) and then adjust the accidentals for the quality. Measured in half steps, each quality has a formula.
Major and minor, and the other two
Only major and minor triads can be the tonic of a piece: their perfect 5th makes them stable. The diminished triad occurs naturally on VII in major and plays a supporting role to the dominant. The augmented triad does not exist in the major scale and usually arises in passing.
The augmented triad has another oddity: all its thirds are equal, so C–E–G♯, E–G♯–B♯ and A♭–C–E sound alike. Only the spelling and the context say which is the root.