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What’s the difference between C2, Csus2, Cadd2, C9 and Cadd9?

C2 Csus2 Cadd9 C9 Cadd9

The humble chord name; it conveys so much information with just a few letters and numbers. Most of the music we see as a guitarist, whether it be a lead sheet, lyric sheet, tablature or full score contains chord names. But are you really playing the right notes? There is no clear naming standard across all genres of music. So, it’s difficult to know.

The C2, Csus2, Cadd2, C9 and Cadd9 chords seem to be especially tricky with less standardization than others. Let’s dig into this a bit and see what we can work out.

The major scale

The naming of all chords begins with the major scale. Even minor chords can be derived from the major scale, so this is the place to start.

Just as in any basic article about scales and chord structures, we’ll use the Key of C in the examples (yes, yes, I know sharps and flats exist in the real world, but for understanding the concepts, let’s keep it as simple as possible).

Here is the key of C, with the degrees of the scale noted above.

1234567
CDEFGAB

The basic major chord is constructed from the 1, 3 and 5 of the scale, so C, E and G for a C major chord (also known as just C). Every C major chord will contain these notes and only these notes. If it has more notes, it’s not a C major, if it has different notes, it’s not a C major.  Simple enough, right?

To extend chord names beyond a basic major or minor we continue the numbering by repeating each note twice.

1234567 891011121314
CDEFGAB CDEFGAB

By using this scale numbering above, we can construct every chord.

Constructing the chords

Let’s construct the C2, Csus2, Cadd2, C9 and Cadd9 chords, by changing and adapting the C major chord.

C major = C, E, G

2 or 9

The numbering system above shows the 2 is a D and the 9 is also a D. So, all of the chords we’re considering contain a D . . . but, as you’ll see, it’s not necessarily that simple.

Sus

The sus in a chord name standards for “suspended”.  This chord type creates extra tension by exchanging the 3rd (for a major chord) or a minor 3rd (for a minor chord) for another note.

Some will debate whether the suspended 4th is the only option for a sus chord. They will argue that a sus2 cannot be used.  But, given that sus2 is commonly used by guitarists we will ignore the debate entirely and assume sus2 does exist.

For a sus2 chord, we would replace the 3 of the scale for the 2 of the scale. So Csus2 is just a C major chord with the 2 (D) replacing the major third (E).

Csus2 = C, D, G

Add

When using “add” it literally means to add a note to the chord. Cadd9 would be a C major with the 9 (D) added. As 2 and 9 are both D, the add2 and add9 chords would be constructed as follows.

Cadd9 = C, E, G, D

Cadd2 = C, D, E, G

The notes in these chords are the same, but the order is different. There is an important distinction (keep reading to find out why).

Without sus or add

Where there is no sus or add, the rules of basic chord construction come into play.

Chords are constructed from notes in steps of 2. The major 9 chord would be constructed with the 1, 3, 5, 7, 9 notes of the scale, the major 11 chord would be constructed with the 1, 3, 5, 7, 9, 11 notes of the scale.

When using the Key of C, the 1, 3, 5, 7 of the key are C, E, G, B. This is known as a C major 7 chord.  C major 9 would be a C major 7 with a 9 added.

C major 9 = C, E, G, B, D

When the 7 of the scale is flattened by one semi-tone it is known as a dominant 7. Often the word dominant is dropped and the chord is just referred to as C7. C9 (or C dominant 9) would be a C7 with a 9 added.

C9 = C, E, G, Bb, D

What about the C2 chord?

Finally, we come to the C2 chord. This is the odd one out, all the others follow patterns and rules that we can understand. But, not so with C2. This is the cause of so much confusion.

Usually, C2 is used to indicate a C major with a D added. Yep, you guessed it, it has exactly the same notes as the Cadd9, or the Cadd2. I say “usually”, because I have equally seen it used in place of a Csus2.

So, even though Cadd2 and Cadd9 contain the same notes, C2 and C9 never have the same notes, and that’s just confusing.

Personally, I avoid C2 as a chord name. It just doesn’t fit with the “rules”. I prefer to stick the sus and add systems.

Getting technical?

Above, we saw that Cadd9 and Cadd2 have the same notes, but in a different order.

Cadd2 = C, D, E, G

Cadd9 = C, E, G, D

The notes may be the same, but the voicing of these chords is subtly different. The 9 indicates the D is an octave + 1 tone higher than the bass, whilst the 2 is just 1 tone higher than the bass.

Due to the way a guitar is constructed, it is almost impossible to build some chords with the notes in the right order. Add2 is one of those almost impossible chords. But add9 (with the D an octave higher than the bass) is much easier to build. Whilst there is a distinction, on a guitar we normally need to work with whatever we can, so we might treat add2 and add9 as the same chord. Really, we shouldn’t as the highest note and lowest notes in the chord can drastically change the feel of the chord.

I know what you’re thinking, if add2 and add9 exist, does this mean that Csus9 exists? I suppose so, though I don’t believe I’ve ever seen it.

Most of us don’t think about guitar this way. We associate the chord names with the shapes we play. But once we realize the order of the notes changes the feel of the chord we will cease to see the chords as just shapes, but a harmony of individual voices all coming together.