Chords are stacked intervals, nothing more

Take a note, skip a letter, take the next one. Every chord you will ever play is built with that one move, repeated.

A chord is three or more notes played together. That much is obvious from hearing one. What is less obvious — and what makes every chord name suddenly readable — is how they are built.

This is step five of the music theory path. It assumes you know what intervals are, because chords are made of them.

Chords are stacked thirds. Take a note, skip a letter, take the next one, skip another letter, take that one. Three notes, and you have a chord.

The triad

Those three notes have names. The one you started on is the root — it gives the chord its letter. The middle note is the third. The top note is the fifth. Root, third, fifth. Every basic chord you will ever play is some version of these three.

A three-note chord like this is called a triad, and there are only four kinds. The difference between them is which sort of third goes where.

Major and minor differ by one note

This is the single most useful fact in harmony. C major is C, E and G. C minor is C, E flat and G. The root is the same. The fifth is the same. The only thing that changed is the middle note, moved down by one semitone.

One semitone is the entire emotional distance between bright and dark in Western music. Try it on your instrument — play a major chord, drop the middle note a fret or a key, and listen to what happens.

Everything else about the chord is unchanged. That is worth sitting with, because it tells you the third is the note carrying the character, and the root and fifth are structure.

Adding a fourth note

Keep stacking thirds and you get a seventh chord. Root, third, fifth, seventh — four notes instead of three.

Sevenths are where chords stop sounding like textbook examples and start sounding like music. A plain C major is stable and a little plain. A C major seventh is warm and slightly wistful. A C dominant seventh is restless and wants to move somewhere.

That restlessness is not a metaphor. The dominant seventh contains a tritone, the most unstable interval there is, and the ear genuinely wants it resolved. It is the engine that drives most chord progressions home.

Inversions

You do not have to play the root at the bottom. C E G is the same chord as E G C or G C E — the same three notes, reordered. These are called inversions.

This matters practically more than theoretically. Inversions are how you move between chords without your hand jumping around the instrument, and how a bass line moves independently of the harmony above it.

Chords belong to keys

Chords are not free-floating. Build a triad on each note of a major scale using only notes from that scale, and you get seven chords — three major, three minor, and one diminished, always in the same order.

In C major those are C, D minor, E minor, F, G, A minor, and B diminished. Those seven chords are the vocabulary of that key, and most songs in C use very few notes outside them.

This is what the circle of fifths is showing you when it displays a key. And it is why a chord can belong to several keys at once — the overlap between keys is exactly what makes changing key possible.

What to do with this

Learn the four triad types by their interval recipe rather than by memorising shapes. Four plus three is major, three plus four is minor. Once that is automatic, you can build any chord on any instrument without looking anything up.

Then use the chord finder to check yourself. Pick a root, pick a quality, work out the notes in your head first, then look.

Next: progressions — why chords move where they move.