Chords: notes stacked in thirds

A chord is more than one note at once. That is the whole definition. What makes chord theory worth learning is not the definition but the fact that the useful ones are built to a pattern, and once you see it you stop memorising.

Skip a note, skip a note

Take a scale and pick every other note. Starting on C in C major: C, skip D, E, skip F, G. Those three make a C major triad.

• C
• add the 3rd
• add the 5th

Do the same starting on any other note of the scale and you get that note's chord. Every one is a stack of two thirds, and whether each third comes out major or minor depends on where the scale's semitones fall.

That single key is the whole difference between the two chords everyone calls happy and sad. Nothing else moves. Play them back to back and the change is obvious, which is a fair summary of why theory is worth half an hour: the names are complicated and the thing itself is not.

• major
• minor

Keep stacking

Add one more third on top and you have a seventh chord. This is where music starts sounding less like a hymn and more like a record.

• C
• C major 7
• G7
• D minor 7

That G7 is worth sitting with. It contains a tritone, between the B and the F, and that tritone is unstable enough that the chord sounds like it is leaning somewhere. Play G7 and then C and you will hear it arrive.

The chords of a key have jobs

Musicians number the chords of a key with Roman numerals, so that a progression can be talked about without naming a key at all. In C major:

• I C
• ii Dm
• iii Em
• IV F
• V G
• vi Am

I is home. V is the one that pulls hardest back to home. IV is a step away from home that feels open rather than tense. vi is the relative minor, the same notes as I seen from a darker angle.

Those four carry an enormous amount of popular music. I, V, vi, IV in particular has been the backbone of so many hits that a comedy band built an entire act out of playing them in sequence, and the joke works because the observation is true.

Inversions, or: stop jumping your hand around

A chord is still itself if you move its notes into a different order. C major is C E G, but it is also E G C, or G C E.

• root position
• 1st inversion
• 2nd inversion

This is the single most useful practical trick on this page. Playing C then F then G in root position means throwing your hand around the keyboard. Play C as C E G, F as C F A, G as B D G, and your hand barely moves. It also sounds better, because the notes stop leaping about.

There are shapes and fingerings on the piano chords page, and the guitar's own version of this problem on first guitar chords.