 What is an Extension ?

All the chords we have looked at so far in the key structure of C Major have been made up of three notes. This is called a Triad.

An extension is where you add other notes from the scale to the basic triad to make a four note or five note or six note chord.

So for example we can 'extend' the chord of C major by adding a B note to the basic triad - this gives us a C major 7th chord.

Look at the scale of C with numbering This may seem a bit like a math lesson but stick with it - this is all useful stuff!

By taking every other note you get the main chords i.e. - starting with C

1 + 3 + 5 = C major [ C ]

1 + 3 + 5 + 7 = C major seventh [ Cmaj7 ]

1 + 3 + 5 + 7 + 9 = C major ninth [ Cmaj9 ]

Same C major scale with the numbering starting on D 1 + 3 + 5 = D minor [ Dm ]

1 + 3 + 5 + 7 = D minor seventh [ Dm7 ]

1 + 3 + 5 + 7 + 9 = D minor ninth [ Dm9 ]

Same C major scale with the numbering starting on G 1 + 3 + 5 = G major [ G ]

1 + 3 + 5 + 7 = G seventh [ G7 ]

1 + 3 + 5 + 7 + 9 = G ninth [ G9 ]

1 + 3 + 5 + 7 + 9 + 11 = G eleventh [ G11 ]

1 + 3 + 5 + 7 + 9 + 11 + 13 = G thirteenth [ G13 ]

Although technically this G 13 is made up of the notes shown - you can't get that many notes on guitar so in practice you would leave out the 11th and possibly the 5th .

A common G13 chord on guitar is 1 + 3 + 7 + 9 + 13 All these chords belong in the Key Structure of C Major

An Example of the Use of Extensions
By using extensions you can add ' movement ' to basic chords - play these 2 bars : -

| C / / / | Am / / / |

Then play these 2 bars : -

| C / Cmaj7 / | Am / Am7 / |

The same basic chord sequence but the second example has more movement than the first.

Exercise

I'm sure you can work out for yourself the rest of the chord extensions in the key structure of C Major using the method outlined above.
Remember this is theory and is useful to overall musicianship so the fact that you might never need or want to play a G13 or other highly extended chord shouldn't put you off !
B minor b5 only extends to B minor 7 b5 for all practical purposes - This extension [ Bm7b5 ] is more commonly used than the basic triad.