3.1 Triads

Building a triad

A triad is a three-note chord built in thirds: a root, a third, and a fifth. C–E–G is a C major triad.

Four qualities

Major = major 3rd + perfect 5th; minor = minor 3rd + perfect 5th; diminished = minor 3rd + diminished 5th; augmented = major 3rd + augmented 5th.

Triads on scale degrees

In a major key, the triads are: I, ii, iii, IV, V, vi, vii° — major on 1, 4, 5; minor on 2, 3, 6; diminished on 7. Uppercase = major, lowercase = minor, ° = diminished.

Key terms

Triad

three-note chord: root, third, fifth

Major triad

major 3rd + perfect 5th

Minor triad

minor 3rd + perfect 5th

Diminished / augmented

min3+dim5 / maj3+aug5

Major-key triads

I ii iii IV V vi vii°

Try an AP-style question

A major triad consists of…

1. two stacked minor thirds
2. a M3 and P5 above the root
3. two stacked major thirds
4. a m3 and P5 above the root