The add9 chord is a major chord with the ninth tone in the scale added and is a so-called added tone chord, more commonly referred to as a add chord. If we take the C major chord as an example, it consists of C, E and G. If we add a D we have a Cadd9 chord with the notes C, E, G and D.
You must separate this chord from the Dominant ninths that are written like C9. The difference is that a dominant 9th is made by expanding a seventh chord with the ninth, like C, E, G, Bb and D forms a C9. In an add9 chord the seventh is missing and the ninth is added to a triad.
Chord progressions with add9 chords
Add9 chords aren't one of the most common chord categories, but they truly exist in lots of songs. A very nice sequence comes from varying Cadd9 with a G major. You could when for example add a D major and you get something like this (used in the Green Day song "Time of Your life"):
G – Cadd9 – D
Another progression, including Dadd9:
G – C – Dadd9 – D7/F# – G
A third progression, including several add chords:
Fadd9 – Eadd9 – Dm7 – Aadd9
Minor add chords
Less common are the minor add chords. We can compare add9 and madd9 to see what notes are different. In Cadd9 we have C, E, G and D in comparison with Cmadd9 with C, Eb, G and D.
The presented diagrams are mixed with both open shapes and barre forms (Amadd9 and Bmadd9). The latter is movable and based on the Emadd shape.
An example is:
Emadd9 – Am9 – Dadd9 – G6
A suggestion is to play Am9 as X05500.
Another minor add chord in short notation:
Bbm add9 68 10 666
These two shapes are, for example, used in the famous song "Every Breath You Take" with The Police. The chord sequence is:
Gadd9 - Emadd9 - Cadd9 - Dadd9 - Add9
When playing the progression of the song, use finger picking and if you can't manage the stretch in Gadd9 and Add9, you can move the index finger from the 6th to the 3rd string during the playing.
Notice the similarities between Cadd9 and Dadd9 with the open Aadd9 shape above.
Sus add chords
Since add and sus chords can be close related, and in fact be identical in some occasions, are chord names sometimes written as sus (add9).
The relationship between suspended and added tone chords
between suspended and added tone chords are closed. We can compare Cadd2, Cadd9, Csus2 and Csus4. The difference is that in added tone chords, a tone is added and in suspended
chords, a tone is exchanged. See also add2.
Chord constructionCadd2 x - C - E - G - D - G
Cadd9 x - C - E - G - D - E
Csus2 x - C - D - G - C - E
Csus4 x - C - F - G - C - x
Guitar versions of the chord
Notes in chordCadd2 C - D - E - G
Cadd9 C - E - G - D
Csus2 C - D - G
Csus4 C - F - G
Theoretical order of notes
As could be notice in the examples above, there are no important differences concerning the chord construction between Cadd2 and Cadd9. This is due to the instrument and the problems to find a shape that match perfect. To separate the chords, it would be correct to have the D tone early and late in Cadd2 and Cadd9 respectively.
Even that there are differences, sometimes an add and a sus chord with the same root tone can be played with the identical guitar chord. An example is Aadd9 and Add2. This is because the C# is omitted in Aadd9 because both B and C# would fit in the same shape as an open chord.