Chords in the key of C major

The scale is C D E F G A B. A triad on each degree gives:

I — C major (C E G). Home.

ii — D minor (D F A). Approaches G; the ii of the ii–V–I.

iii — E minor (E G B). Shares two notes with C and two with G, so it slides between them almost invisibly.

IV — F major (F A C). The subdominant, and on guitar the reason this key is harder than it looks.

V — G major (G B D). Pulls home, more strongly as G7.

vi — A minor (A C E). The relative minor, sharing all seven notes.

vii° — B diminished (B D F). Rare in songs; G7 does its job with less trouble.

With sevenths these become Cmaj7, Dm7, Em7, Fmaj7, G7, Am7 and Bm7♭5 — the standard set in jazz, where G7 to Cmaj7 is the cadence everything else is measured against.

C–F–G (I–IV–V). The three chords of countless songs, and the first progression most people learn on any instrument.

C–Am–F–G (I–vi–IV–V). The fifties progression in its original key. If a doo-wop song comes to mind, it is probably this.

C–G–Am–F (I–V–vi–IV). The modern pop loop. The same four chords as above in a different order, and it sounds like a different decade.

Am–F–C–G (vi–IV–I–V). Starting on the relative minor puts the same harmony in shadow.

Dm–G–C (ii–V–I). The jazz cadence. Play it as Dm7–G7–Cmaj7 and the key announces itself.

C–Em–Am–F. A gentler descent than I–V–vi–IV, using the third degree to soften the fall from C to Am.

On paper C major is the simplest key there is: no sharps, no flats, and at the piano nothing but white keys. Every theory example is written here for exactly that reason.

On guitar the picture changes. C major itself is an awkward stretch for a beginner, F major demands either a barre or a compromise shape, and neither rings with open strings the way G, D and Em do. The result is that guitarists learn the theory in C and play the songs in G — and then wonder why the two never seem to line up.

The practical answer is a capo. Put it at the fifth fret and play G shapes: the sound is C major, the fingering stays easy, and the numbers are still I–IV–V. Many recordings you assume are in G are exactly this.

At the keyboard the opposite holds: C is the natural home, and moving away from it is what takes practice.

Three chords from outside the key turn up so often in this key that they hardly count as departures.

B♭ major, the flat seventh, borrowed from C minor. It gives the rock sound of C–B♭–F, where the ear expects Bdim and gets something solid instead.

A major instead of Am — a secondary dominant pulling to Dm. Common in folk and in anything with a hint of the older repertoire.

F minor instead of F. The minor fourth is the single most reliable way to make a progression ache: C–F–Fm–C is a whole emotional turn in four chords.

Each of these leans out of the key for one chord and returns. That is a different thing from changing key, and the difference is worth hearing clearly — see modulation for when the departure becomes permanent.

A minor is the relative minor and shares every note, so a song can sit in both at once — verse in Am, chorus in C — without a single accidental.

G major is one sharp away and is the most common destination for a key change upward; F major is one flat away in the other direction. These three keys together cover an enormous amount of the popular repertoire, and moving between them costs one note each time.

If a song in C sits badly for your voice, the fix is arithmetic rather than rewriting: read the progression as numbers, then play those numbers in a key that fits. I–vi–IV–V in C is C–Am–F–G; in G it is G–Em–C–D; in D it is D–Bm–G–A. The song does not change — only its height does.

C major is the key theory is taught in; the key of G is the one guitarists play in, and the gap between them is worth hearing. Its relative minor, A minor, sits with the other minor keys, and moving a song to a key that fits a voice is transposition.