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Major and minor: one note of difference

People describe major as happy and minor as sad. That is close enough to be useful and wrong often enough to be worth qualifying. What is exact is the mechanism: one note, one semitone.

Move the middle note

A basic chord is three notes: the root, something a third above it, and something a fifth above it. Keep the outer two where they are and shift the middle one down a semitone. That is the entire difference.

Play them one after another a few times. The bottom note is the same. The top note is the same. Only the one in the middle moved, and by the smallest distance available.

I find this a bit unreasonable every time. A semitone is nothing, and the change in mood is total.

C major: the white keys, and nothing else.

C minor: three of them slide down a key. The third, the sixth and the seventh.

Three notes move, not one, and the third is the one doing most of the work. Drop only that and you already hear it turn; the other two decide how far it goes.

Why it lands so hard

Go back to overtones for a second. A vibrating string carries a stack of frequencies above the note you played, and the major third is fairly high up that stack but genuinely there. When you play a major chord you are reinforcing something the root note was already producing.

The minor third is not in that stack in any simple way. It sits against the overtones rather than with them. That is not a complete explanation of why a whole culture hears one as bright and the other as dark, and anyone who tells you it is has skipped a step. But the acoustic asymmetry is real, and it is not nothing.

The happy and sad thing

It falls apart quickly once you listen around. Plenty of minor-key music is not sad at all. Most klezmer, a good deal of flamenco, and a great many Irish reels sit in minor or modal keys and are played at parties.

A better description than happy and sad is open and closed, or bright and shaded. Tempo and rhythm do at least as much of the emotional work as the third does.

Both live inside one key

Here is the part that surprises people. If you build a chord on each note of the C major scale, using only white keys, you do not get seven major chords. You get three major, three minor and one odd one out.

Nobody chose that. It falls out of the uneven gaps in the major scale, where two of the seven steps are semitones and five are tones. The pattern of majors and minors is the same in every key, which is why a chord progression can be moved to a new key and still work.

More on the family and its jobs on the chords page.