Major vs minor chords

A triad is three notes: a root, a note a third above it, and a note a fifth above the root. The fifth is the same in both major and minor. Everything hinges on the third.

The two shapes

Major triad — root, major third, perfect fifth. From the root: 0, 4, 7 semitones.

Minor triad — root, minor third, perfect fifth. From the root: 0, 3, 7 semitones.

One note. One semitone. That is the whole difference.

Another way to see it

Stack two thirds and read them in order:

• Major = major third, then minor third on top
• Minor = minor third, then major third on top
• Diminished = minor third, then minor third
• Augmented = major third, then major third

Diminished and augmented are less common but built the same way. Diminished has a flattened fifth and sounds unstable; augmented has a raised fifth and sounds suspended in mid-air.

The "happy vs sad" thing

It is the standard shorthand and it is not wrong, but it is not the whole story either. Minor chords carry plenty of music that is not sad — a great deal of dance music is in minor keys. Tempo, rhythm, register and context do at least as much work as chord quality.

What is reliably true is that the major third is brighter and the minor third darker. Emotion is what a listener builds on top of that.

Chords in a key

Build a triad on each degree of a major scale using only notes from that scale, and the qualities fall into a fixed pattern:

In C major: C, Dm, Em, F, G, Am, B°.

This pattern holds in every major key, which is why chord progressions transpose so cleanly. A I–V–vi–IV progression is C–G–Am–F in C major and G–D–Em–C in G major. Same relationships, different letters.

Hearing the difference

Play the two chords back to back and the shift is unmistakable. Naming one in isolation, with no reference, is harder — that is a trained skill, not an obvious one.

Start with the interval rather than the chord: if you can hear a major third against a minor third, chord quality follows almost immediately.