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 why C – Am – F – G is the same song shape as G – Em – C – D. It is how players call changes, move a song to a singer’s range, 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 C that is C · Dm · Em · F · G · Am · B°. You already own six of those seven from Open chords; only B° is new, and songs rarely use it.
The keys you will meet first
Read down a column to transpose: the IV of every key, the V of every key. C and G are nearly all open shapes; in F, B♭ is the partial barre from Barre.
| Key | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| C | C | Dm | Em | F | G | Am | B° |
| G | G | Am | Bm | C | D | Em | F♯° |
| F | F | Gm | Am | B♭ | C | Dm | E° |
| D | D | Em | F♯m | G | A | Bm | C♯° |
| A | A | Bm | C♯m | D | E | F♯m | G♯° |
Progressions by number
The same few number patterns run through most popular music. Each plays in C, two strums a chord.
- I – IV – V – I — C F G C. Folk, country, rock and roll — the three-chord song.
- I – V – vi – IV — C G Am F. The pop loop under hundreds of songs.
- vi – IV – I – V — Am F C G. Same four chords, starting on the minor — it sounds sadder.
- I – vi – IV – V — C Am F G. The 1950s doo-wop turn, and the first loop on Open chords.
- ii – V7 – I — Dm G7 C. 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 C: G7 → C, where the F in G7 falls to the E in C. The same trick points at any chord — E7 → Am leans into the vi.
Minor keys
Every major key has a relative minor on its vi: Am for C, Em for G. 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 C–F–G shapes, and you are playing I–IV–V in D (D–G–A). Use the table to find what a singer’s key needs, then pick the capo that lets you keep 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: C F G Am → C. G C D Em → G. 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, F, D and A 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.