A Guide To Guitar Chords

Guitar Music Theory 3


Until now we constructed chords by stacking thirds on top of each other. The resulting triads or seventh chords form the basis. Other notes can be added to these basic chords, notes that we call extensions.

The C major scale (again):

C Major Scale C    D    E    F    G    A   B
1    2    3    4    5    6   7

Construct a chord on C --> Cmaj7:

C    E    G    B
1    3    5    7

We use 4 notes in this chord, what means that there are 3 notes left from the C major scale: 2, 4, 6.If one or more of these notes become part of the chord, we call them extensions or chord extensions.

Usually extensions are played one octave higher compared to the chord tones. This benefits the clarity of the chord.

Let's add an octave to the extensions:

  • 2 becomes 9 (2+7(one octave)=9)
  • 4 becomes 11
  • 6 becomes 13

Let's apply this to Cmaj7: Add 2 to Cmaj7 and we get Cmaj9

C    E    G    B    D
1    3    5    7    9

Maybe major chords are not a very good example to explain extensions because the two other tensions that are left, 4 and 6, behave in a special way in combination with major chords.

The first thing we have to look at are avoid notes : extensions that are a half step above a chord note. These notes sound very disharmonic in the chord so they are almost never used, only in case the disharmonic sound is wanted as an effect.
The 4 of the C major scale is a half step above the 3 (chord tone) of that chord (f is a half step above e) --> the 4 is an avoid note for major chords.
A possible way to deal with this is raising the 4 half a note : f turns into f# and is no longer an avoid note. The basic scale is no longer C major (C Ionian) though, but C Lydian (a kind of guitar scale or mode).  We call this chord a Cmaj7(#11).

The 6 also behaves differently in combination with major chords.  When we add the 6 to a major chord we don't play the 7 and there is no octave added to the 6. This is because the 6 and 7 sound too close to each other.

Add 6 to C major and we get a C6 :

C    E    G    A
1    3    5    6

The same happens to the 6 in combination with minor chords : the 7 is not played.
Add the 6 to Dm7 and we get Dm6 (watch out : the 6 is no longer the note a because the root of the chord changed to D.  The six of D is B (D E F# G A B C#) :

D    F    A    B
1    b3   5    6

The 4 is not an avoid note for minor chords because it is two half steps away from the b3 and not one half like it is with major chords.
So we can safely add the 4 to Dm7 and we get Dm11:

D    F    A     C      G
1    b3   5     b7    11

The 4 added to a dominant chord is also a special case.
When a 4 is combined with a dominant chord, the 3 of the chord is not played.  We call chords like this sus4 chords.
As a guitar chord sus4 chords are often combined with a 9:

G    C     D      F    A
1    4     5     b7    9

Here's an overview of chord types and possible extensions:

Chord Type Added Note Symbol  
Major 2 Cmaj9  
avoid note
#11 from
lydian scale
6 C6 no 7
Minor 2 Cm9  
4 Cm11  
6 Cm6 no 7
Dominant 2
b2 and #2 from
altered scale
4 C7sus4  
b6 comes from
altered scale


Guitar music theory part 3  Next page: part 4 of guitar music theory