Harmony
Key
A key is the home base of a piece of music: a central note (the tonic), the major or minor scale built on it and the family of chords that scale produces.
What is a key in music?
Saying a song is 'in G major' packs three facts into two words:
- the tonic: G, the note the music settles on;
- the scale: G major, G A B C D E F#, following the pattern of the major scale;
- the chords: the ones you build on each note of that scale.
So a key is not just a list of notes, it is a hierarchy: every note relates to the tonic. That is why a G chord sounds like arriving home and a D7 makes you want to get back there.
Which chords belong to a key?
In G major, stack thirds on each scale degree and you get seven chords:
| Degree | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| Chord | G | Am | Bm | C | D | Em | F#dim |
The three major chords I, IV and V (G, C, D) cover hundreds of folk and rock songs. Add the vi (Em) and you have the pop progression G, D, Em, C. Every major key has a relative minor that shares its notes: for G major, that is E minor.
How do you find the key of a song?
Three methods that work together, from quickest to most reliable:
- Your ear: the chord the chorus ends on, the one that sounds like home, is almost always the tonic.
- The chord list: write out the chords and find the major scale that contains them all. G, C, D, Em: only the notes of G major (or its relative, E minor) fit.
- The dominant: a seventh chord (D7) points to the chord a fifth below it (G).
Watch out for ambiguous loops: Em, C, G, D is in G major if the song settles on G and in E minor if it settles on Em. On sheet music, the key signature is a clue, never the whole answer.
What are the easiest keys on guitar?
The keys that use open strings: E, A, D, G and C major, plus E minor and A minor.
| Key | I | IV | V |
|---|---|---|---|
| C | C | F | G |
| G | G | C | D |
| D | D | G | A |
| A | A | D | E |
| E | E | A | B |
To play in A major with G-shape chords, put a capo on the 2nd fret: G, C, D become A, D, E. To see every key and its neighbours at a glance, use the interactive circle of fifths. When a song moves to a new tonic partway through, that is a modulation.
Key takeaways
- Key = tonic + scale + chord family.
- G major: G Am Bm C D Em F#dim.
- To find it: the home chord, the chord inventory, the dominant.
- Easy guitar keys: C, G, D, A, E, Am, Em; a capo handles the rest.
Frequently asked questions
What is the difference between a key and a scale?
A scale is a sequence of notes (G major: G A B C D E F#). A key is the whole musical context: the tonic as the centre, the scale and the chords built from it. You play a scale; you live in a key.
How many keys are there?
Twelve major and twelve minor keys, so 24 in practice. Counting enharmonic spellings separately (F# major and Gb major, for example), there are 30 written keys with their key signatures.
Does the first chord of a song tell you the key?
Often, but not always. Plenty of songs start on the vi or the IV. Trust the chord that ends the chorus and the one that feels like a point of rest instead.
Related terms
Practise in the workshop
Take it from theory to the fretboard
Open the workshop tools and see this idea across the whole neck. Free account, no card needed.