Some are close relatives: they share their notes, or their root. Knowing which helps you hear how a song is built, and how it can move from one key to another. You met relative and parallel minors in Minor Scales; here's what they mean for keys.
C major and A minor use exactly the same seven notes, so they share their key signature (no sharps or flats). They're relative keys: A minor is the relative minor of C major. The minor key always starts three half steps below the major one.
What differs is the , the note the music feels it has arrived at. The same notes sound bright around C and darker around A. Listen to the same kind of in each key: the built on the 1st, 4th and 5th notes of each scale, then home again. The count those notes; small letters mean minor chords, and Am means A minor.
C major and C minor start on the same note but use different notes: C minor lowers the 3rd, 6th and 7th (E♭, A♭, B♭). They're parallel keys. Switching between them keeps the home note but changes the mood, a favourite trick in pop and film music.
C minor has three flats, the same signature as E♭ major, its relative major. So every minor key is the parallel of one major key and the relative of another.
Songs often move to a new key, called a modulation. Besides the relative key, the smoothest moves are to a neighbour on the : neighbours share six of their seven notes. Here's how many notes each major key changes compared to C major:
| Key | Notes changed | New notes |
|---|---|---|
| C major | 0 | – |
| G major | 1 | F♯ |
| D major | 2 | F♯ C♯ |
| A major | 3 | F♯ C♯ G♯ |
| E major | 4 | F♯ C♯ G♯ D♯ |
| B major | 5 | F♯ C♯ G♯ D♯ A♯ |
| G♭ major | 6 | B♭ E♭ A♭ D♭ G♭ C♭ |
| D♭ major | 5 | B♭ E♭ A♭ D♭ G♭ |
| A♭ major | 4 | B♭ E♭ A♭ D♭ |
| E♭ major | 3 | B♭ E♭ A♭ |
| B♭ major | 2 | B♭ E♭ |
| F major | 1 | B♭ |
G major and F major change just one note each, so a song in C can slip into either almost without you noticing. Here's a move from C to G: the D7 chord (a D chord with one extra note, C; come in the Chords chapter) brings in F♯, the one new note, and pulls the music to its new home, G.
In C major: C D E F G A B. In G major: G A B C D E F♯.
Next: Transposing and the Capo