Chords in a key why songs use the chords they do
A key is a scale, and stacking thirds on each note of that scale gives seven chords that belong together. Number them and every song in every key reads the same — which is how players call changes, transpose with a capo, and guess the next chord before it comes.
Seven chords from one scale
Build a triad on each note of the major scale using only notes from that scale. The qualities always fall in the same order:
I major · ii minor · iii minor · IV major · V major · vi minor · vii° diminished
Capital numerals are major, small ones minor, ° diminished. In G that is G · Am · Bm · C · D · Em · F♯°.
The keys you will meet first
The open-chord keys. Read down a column to transpose: the IV of every key, the V of every key.
| Key | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| C | C | Dm | Em | F | G | Am | B° |
| G | G | Am | Bm | C | D | Em | F♯° |
| D | D | Em | F♯m | G | A | Bm | C♯° |
| A | A | Bm | C♯m | D | E | F♯m | G♯° |
| E | E | F♯m | G♯m | A | B | C♯m | D♯° |
| F | F | Gm | Am | B♭ | C | Dm | E° |
Progressions by number
The same few number patterns run through most popular music. Each plays in G, two strums a chord.
- I – IV – V – I — G C D G. Folk, country, rock and roll — the three-chord song.
- I – V – vi – IV — G D Em C. The pop loop under hundreds of songs.
- vi – IV – I – V — Em C G D. Same four chords, starting on the minor — it sounds sadder.
- I – vi – IV – V — G Em C D. The 1950s doo-wop turn.
- ii – V7 – I — Am D7 G. The jazz cadence — see Jazz.
Why V wants to go home
The V chord holds the scale’s seventh note, a half step under the root, and that note wants to rise. Make it a V7 and the pull doubles. In G: D7 → G. The same trick points at any chord — B7 → Em leans into the vi.
Minor keys
Every major key has a relative minor on its vi: Em for G, Am for C. Same seven chords, different home — the song sounds minor when it starts and ends on the vi. Minor-key songs usually borrow a major V (E or E7 in A minor) for the pull home, which comes from the harmonic minor on Scales.
Transpose with a capo
The numbers do not change; only the names do. Capo at fret 2 and play G–C–D shapes, and you are playing I–IV–V in A (A–D–E). Use the table to find what a singer’s key needs, then pick the capo that lets you use the shapes you know.
Find the key of a song
- Write down every chord in the song.
- Find the row in the table that holds all of them. That is the key (or its relative minor).
- The chord the song ends on — and usually starts on — is home.
Try it: G C D Em → G. A D E F♯m → A. Am F C G, ending on Am → A minor, relative of C.
Ready when
Move on when all of these are true on a normal day, not your best one:
- You can say the I, IV, V and vi of C, G, D, A and E without the table.
- Given a song’s chord list, you can name its key and play it in another key with a capo.
- You can hear when a progression lands on V and expect the I next.