What the key tells you
Saying a song is "in G major" says two things. Its home note is G, and it mostly uses the notes of the G major scale: G, A, B, C, D, E, F♯. Those seven notes give you seven chords, and most popular songs get by with three or four of them.
Knowing the key helps you find chords by ear, transpose chords to suit your voice, or put a capo in the right place.
Step 1: find the home note
Listen to the song and stop it at the end of a chorus, or at the very end. Hum the note that seems to "finish" the phrase, the one you could stop on without feeling let down. It's almost always the tonic, the note that gives the key its name.
A simple test: hold that note while the song keeps going. If it sounds good over most of the chords and feels "at home" at the resting points, you've got it. If it rubs all the time, try another note.
Now you need to name it. Find it on your instrument, or hum it to Fredon: the app recognizes the sung note live and displays it, in C D E or do re mi.
Step 2: check with the chords
If you already have the chord chart, three clues usually point the same way:
- The last chord. Songs very often end on the tonic chord. The first chord often is too, but less reliably.
- The most frequent chord. The one that comes back at the end of phrases and in the chorus.
- The chord right before the return. Just before the tonic, you'll often find the chord built on the fifth note of the scale. In G, it's D or D7 that leads back to G.
Watch out for traps: some songs fade out, others end on an unexpected chord for a surprise. Trust all the clues together, not just one.
Step 3: major or minor?
Every major scale shares exactly the same notes with a minor scale, its relative minor. C major and A minor (Am) use the same seven notes, no sharps or flats. So do G major and E minor (Em). The relative minor sits three half steps below the major tonic.
So the two keys share the same chords: what changes is the chord the song rests on. If the song keeps coming back to Am and settles there, it's in A minor. If it settles on C, it's in C major. To the ear, minor sounds darker, more melancholy, but that's not a hard rule: trust the home note.
Another clue: in minor keys, the chord on the fifth degree is often played as a major chord. In A minor, you'll often hear E or E7 rather than Em, with its G♯ pulling toward A.
Step 4: read the key signature, if you have sheet music
The key signature is the sharps or flats at the start of each staff. They're always added in the same order.
- Sharps: F, C, G, D, A, E, B. The major key is a half step above the last sharp. One sharp (F♯): G major. Three sharps (up to G♯): A major.
- Flats: B, E, A, D, G, C, F. The major key is the second-to-last flat. Two flats (B♭, E♭): B♭ major. The one exception to remember is a single flat: F major.
- Nothing: C major or A minor.
The key signature always gives you two candidates, the major key and its relative minor. To decide, go back to step 3: look at the last note of the melody and the last chord.
The chords in a key: I, IV, V and vi
The chords in a key are numbered with Roman numerals, after the scale note they're built on. In major, the pattern is always the same:
- I, IV and V are major. They're the pillars: thousands of songs run on these three chords.
- ii, iii and vi are minor. The vi, the relative minor, is the fourth most common chord.
- vii° is diminished, and rare in pop songs.
In G major, I IV V vi give you G, C, D and Em: four easy open chords, and an impressive number of songs.
Common guitar keys
On guitar, people mostly play in keys where the main chords exist as open shapes. Here are their chords:
| Key | I | ii | iii | IV | V | vi |
|---|---|---|---|---|---|---|
| C major | C | Dm | Em | F | G | Am |
| G major | G | Am | Bm | C | D | Em |
| D major | D | Em | F♯m | G | A | Bm |
| A major | A | Bm | C♯m | D | E | F♯m |
| E major | E | F♯m | G♯m | A | B | C♯m |
| F major | F | Gm | Am | B♭ | C | Dm |
In minor, three keys dominate on guitar: A minor (Am, Dm, E or Em, with C, F and G), E minor (Em, Am, B or Bm, with G, C and D) and D minor (Dm, Gm, A or Am, with F, B♭ and C).
If a song is in an awkward key, like B♭ or E♭, a capo lets you keep simple shapes: B♭ can be played with A shapes and a capo at the 1st fret.
What if all you have is the melody?
That's the case with a tune stuck in your head, or a melody you're writing. Sing it, find the home note, then try the I, IV and V chords of that key under each phrase.
Fredon's Melody mode does this from your voice: sing the tune, up to sixty seconds, and the app transcribes it, finds the key and suggests a chord progression, with alternatives and a recommended capo. A good way to check your own analysis, or to write a song.
FAQ
Can a song change key?
Yes, that's called a modulation. The classic case: the last chorus goes up a half step or a whole step. The chords all shift by the same amount.
Are key and scale the same thing?
Almost. The scale is the list of notes; the key adds the idea of a center, the note everything gravitates toward. C major and A minor have the same scale but not the same key.
Why does one chord chart say Re where another says D?
It's the same chord, written with solfège names, as in France, Spain, Italy or Latin America, instead of letters. The full conversion is in the guide do re mi vs C D E.