The four triads – free music theory course

A chord is at least three different pitches heard together. The simplest and most important of all is the triad: three notes stacked in thirds. The note it is built on is the root; above it come the third and the fifth.

On the keyboard, “stacking thirds” means: every other white key. C–E–G, D–F–A, E–G–B… Put your right hand down with fingers 1-3-5 and you are already playing a triad.

Four qualities, two thirds

There are two kinds of thirds: the major third (4 semitones, C→E) and the minor third (3 semitones, C→E♭). Combining these two building blocks gives exactly four triads:

Triad	Lower third	Upper third	Fifth	On C
Major	major (4)	minor (3)	perfect (7)	C – E – G
Minor	minor (3)	major (4)	perfect (7)	C – E♭ – G
Diminished	minor (3)	minor (3)	diminished (6)	C – E♭ – G♭
Augmented	major (4)	major (4)	augmented (8)	C – E – G♯

The numbers in brackets count semitones from the bottom note. Listen to each chord:

C major: bright and stable.

C minor: darker, wistful. Only the third has changed!

C diminished: tense and unstable, it “wants” to go somewhere else.

C augmented: strange and suspended, like a question with no answer.

Here are the four triads in a row on the staff:

M:4/4
L:1/2
K:C
"C"[CEG]2 | "Cm"[C_EG]2 | "Cdim"[C_E_G]2 | "C+"[CE^G]2 |]

Tip: remember that the third decides between major and minor, and the fifth decides between “normal”, diminished and augmented. Major and minor share the same perfect fifth.

Common mistake: thinking a minor chord “has black keys in it”. D minor (D–F–A) is all white keys, while D major (D–F♯–A) has a black one. Intervals are what count, not the colour of the keys.

Explore

Pick a root and a quality, listen, compare: