Chords can be very simple or can become very complex. 

Technically, a chord only needs two notes (if you count a powerchord as a chord), but usually you need 3 notes to call it a chord in the traditional sense. 

Triads and 7th chords are usually seen as fairly simple and basic 3 note and 4 note chords, but when more notes are added to extend the chord, they become more complex. We call those notes added beyond the 7th, chord extensions. 

Chord extensions are notes added beyond the triad and 7th. These are the 9th, 11th and 13th notes in the scale. So for example, a Cmaj7 is a triad with a seventh, but a Cmaj9 is a chord with a seventh and a chord extension (unless it says “add” the 7th is assumed, and the 9th note in the scale of Cmaj is the extension). If the chord name includes “add” then it’s a triad with no 7th, plus the 9th as an extension. 

C add9 = C major triad + 9th

Cmin add9 = C minor triad + 9th

Cmaj9 = C major + 7th + 9th

Cmin9 = C minor +7th + 9th

What type of music uses chord extensions?

Jazz is one of the best examples of a genre of music that heavily uses chord extensions. That’s why many guitarists call chords with extensions “jazz chords”. However, chord extensions are used in all kinds of genres. 

How different genres might approach using chord extensions

To help put chord extensions in songs this usually requires following some arrangement best practices, and different genres might approach this differently. Some might divide the chord across many instruments, while others might play the entire chord on the guitar including the extensions. Chord extensions might also be used for texture and ambience on synth pads.  

Here’s some examples.

Jazz

Jazz guitar usually uses a very clean tone (no distortion), guitarists often layer chord extensions on top of what the bass is doing (which is usually emphasizing the root note of the chord). When the band plays together you will be able to hear the entire chord spread across many instruments, with the bass at the root and the guitar focused on playing the rest of the notes including the extensions, rather than the full chord with the root note. 

Spreading the chord and extensions across multiple instruments keeps the guitar from conflicting with the bass, and allows the extensions to be heard and appreciated. 

Rock & Metal

From my experience, rock and metal guitar players sometimes use chord extensions both with clean and with distortion depending on the song and what they are going for. 

What they often do to help increase clarity when using distortion is play a powerchord with one additional note being the chord extension note. 

A great example of this is the 9th on top of the powerchord. This gives it a sort of melancholic dark sound which is usually great for these genres and it still sounds pretty clear even with distortion. Deftones uses this quite a bit. 

Prog

If you go into the crazier branches of rock and metal like the more progressive stuff, you are more likely to hear chords with chord extensions, both with and without distortion, as this genre can often take influence from classical, jazz and jazz fusion. 

Pop

Chord extensions are also very common in pop, sometimes they are obvious and sometimes they are hidden. They might put the chord extensions on a synth or synth pad in the background  for ambience and texture while the instruments that take the main focus play something more basic, providing a solid foundation for the extensions to rest on. 

However, this approach can be found in pretty much any genre as it is a great production and arrangement trick that works on a wide range of songs. 

Many pop songs are much more musically complex than you realize, but they try to hide the complexity so that it will be easy to understand and listen to. 

Remember the goal of pop music is to appeal to the general public, the widest amount of people possible. 

That’s why you don’t hear mainstream pop get too weird or nerdy with theory, unless they get weird but keep it subtle. 

What do chord extensions do?

Chord extensions can have several functions. Since they add more notes to basic chords, they can define a chord and make it more specific, they can also add more layers of sound which can make the chord sound bigger and more harmonically interesting. This can be used to build tension in a song, provide an added layer of emotion or mood, or make a chord progression flow better and become more interesting. 

Types of chord extensions

There’s 3 types of chord extensions you can add to a triad. These are the 9th, 11th and 13th. All of them correspond to notes within the scale but an octave up, so 9th is the same as a 2nd, 11th is the same as a 4th and 13th is the same as a 6th. A chord is considered to be an extended chord when there are notes added beyond the triad and 7th note. 

Notes such as the 8ths, 10ths, and 12ths are not considered chord extensions since they are the same notes of the triad but an octave up (8th = root, 10th = 3rd, 12th = 5th), so they do not add any new harmonic content. 

How to play chord extensions

If you wish to play chord extensions you will need to build a basic triad chord with or without a seventh and add to it a 9th, 11th, or 13th note from the major scale.   

Let’s look at an example using a Cmaj9.

Notes of C Major scale

C, D, E, F, G, A, B

Notes of Cmaj7 chord

C, E, G, B

Root, 3rd, 5th, 7th

Notes of Cmaj9 (the 7th is included automatically because it doesn’t say “add”)

C, E, G, B, D (an octave up)

Root, 3rd, 5th, 7th and 9th

***Remember chords with extensions like 9, 11, and 13 always have the 7th unless it says “add” in the chord name, in which case, it’s a triad with the extension added***

Let’s say we wanted to do a Cmin9.

Notes of C Minor scale

C, D, Eb, F, G, Ab, Bb

Notes of Cmin7 chord

C, Eb, G, Bb

Root, flat 3rd, 5th, flat 7th

Notes of Cmin9 (the 7th is included automatically because it doesn’t say “add”)

C, Eb, G, Bb, D (an octave up)

Root, flat 3rd, 5th, flat 7th and 9th

How to play chord extensions on guitar

Major and Minor Triad Chords with Added 9 or 11

Cadd9

C add9 (open chord)
C add9 movable 5th string root
C add9 movable 6th string root

Cmin add9

Cmin add9 (open chord)
Cmin add9 movable 5th string root
Cmin add9 movable 6th string root

Cadd11

C add11 (open chord)
C add11 movable 5th string root
C add11 moveable 6th string root

Cmin add11

Cmin add11 (open chord)
Cmin add11 movable 5th string root
Cmin add 11 movable 6th string root

Major and Minor Triad + 7th Chords with 9, 11, or 13

Cmaj9

Cmaj9 5th string root
Cmaj9 6th string root

Cmin9

Cmin9 5th string root
Cmin9 6th string root

Cmaj11

Cmaj11 5th string root
Cmaj11 6th string root

Cmin11

Cmin11 5th string root
Cmin11 6th string root

Cmaj13

Cmaj13 5th string root
Cmaj13 6th string root

Cmin13

Cmin13 5th string root
Cmin13 6th string root

Wrapping it up

Chord extensions are a really powerful tool for making your chords and chord progressions more interesting. As you read earlier, you can use chord extensions on one instrument or spread them across different instruments playing at the same time. They will also add more interesting moods to your chords.

Keep in mind that the more extensions you use, the more defined the chord becomes, which means you may not be able to switch scales on top of it in your melodies without conflicting with the other notes. 

In contrast if you have a more ambiguous basic chord like just major or minor, your melodies can change around through different major and minor modes and scales with less chances of conflicting notes, because triads have less notes and are less specific. 

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