How does it work?

The idea is that each key has 7 predictive chords. In the key of C, these would be: C major / D minor / E minor / F major / G major / A minor / B diminished

Each chord is assigned a number 1-7

1 = C
2 = Dm
3 = Em
4 = F
5 = G
6 = Am
7 = Bdim

This translates across all keys. Here are examples in Key of E and G.

Example Key of E

Example Key of G

 

Song example

Verse:  | 1 / / / | 4 / / / | 5 / / / | 4 / / / |

Chorus: | 6 / / / | 4 / / / | 1 / / / | 5 / / / |

Bridge: | 4 / / / | 2 / / / | 1 / / / | 5 / / / |

 

Key of C:

Verse:  | C  / / / | F  / / / | G / / / | F / / / |

Chorus: | Am / / / | F  / / / | C / / / | G / / / |

Bridge: | F  / / / | Dm / / / | C / / / | G / / / |

 

Key of E:

Verse:  | E   / / / | A   / / / | B / / / | A / / / |

Chorus: | C#m / / / | A   / / / | E / / / | B / / / |

Bridge: | A   / / / | F#m / / / | E / / / | B / / / |

 

Chord inversions

Accidentals modifying a scale degree are usually written to the left of the number.

Examples

♭7 ("flat 7") represents a B♭ major chord in the key of C or an A♭ major chord in the key of B♭.

Examples in the key of G

F = ♭7 ("flat 7")

C# = ♭5 (“flat 5”)

Cm = -4 (“minor 4”)

Dm = -5 (“minor 5”)

 

Chord inversions or slash chords

Examples in the key of G

G/B = 1/3

D/F# = 5/7

C/G = 4/1

D/G = 5/1

 

Other chord qualities such as major sevenths, suspended chords, and dominant sevenths use familiar symbols:

4^Δ7 = Major 7th

5^sus = Suspended chord

5⁷ = 7th

 

Example in G

4^Δ7 = C^Δ7

5^sus = D^sus

5⁷ = D⁷

 

These would stand to be:

F^Δ7 G^sus G⁷ in the key of C

or E♭ ^Δ7 F^sus F⁷ in the key of B♭.

A superscript ² means "add 2" or "add 9".