I decided to write a few lines about sus4 (suspended fourth) chords because I found that students can get quite confused about them, especially because of the large number of different symbols that are used for these chords in lead sheets.
In sus4 chords, the third of a (major or minor) triad is replaced by the fourth scale tone, i.e. by the note which is a perfect fourth above the root note. OK, here's an example: in a Dsus4 chord, the third of the chord (either F# in a D major triad, or F in a D minor triad) is replaced by a G, which is a perfect fourth above the root D: Dsus4 = d - g - a
Many of you guitar players have probably discovered this chord: XX0233
OK, that was simple, and there is usually not much confusion about such basic sus4 chords. However, it gets a bit more complicated when tensions are added, e.g. D7sus4, D9sus4 or D13sus4. (There is no D11sus4 for because the 11 and the 4 are the same notes.) These chords sound really nice because of their open character. They can either function as dominant chords resolving to a tonic chord, such as in the progression D7sus4 - Gmaj7, or they can be used as static chords with no need to resolve. Check out Herbie Hancock's Maiden Voyage for an example of static sus4 chords.
Let's now take a closer look at sus4 chords with added tensions:
D7sus4 = d - g - a - c
D9sus4 = d - g - a - c - e
D13sus4 = d - g - a - c - e - b
Looking at the chord notes of D9sus4, it turns out that the notes above the root note 'd' spell out an inversion of an Am7 chord: a - c - e - g. So an D9sus4 is equal to an Am7/D (Am7 over D as bass note). Sometimes the note 'a' is omitted, which gives a C/D chord (C major triad over D). For D13sus4 we get an extra note 'b', and the notes above the root spell out an Am9 chord: a - c - e - g - b. So we get D13sus4 = Am9/D, or - if the 'a' is left out - we get Cmaj7/D.
To sum up, we get the following equivalent chord symbols:
D9sus4 = Am7/D ≈ C/D
D13sus4 = Am9/D ≈ Cmaj7/D
These chords can be used interchangeably and they all have the same open sounding character. Here are some useful voicings for these chords:
D9sus4: X 5 5 5 5 5; 10 X 10 9 8 X; X X 12 12 13 12; X 5 X 5 5 3; 10 X 10 12 10 12
D13sus4: X 5 5 5 5 7; 10 X 10 12 12 12
And of course, if you play with a bass or keyboard player, you don't necessarily need to play the root on the guitar, so can use any voicing of C, Cmaj7, Am7 or Am9 to get the right sound. Have fun experimenting with these chords!
In the next post I talk about an easy way to improvise over these chords.