Scale modification in sus2 and sus4 chords

Question

I've recently been looking at what makes chords what, and hence my first target for this was looking at major, minor, sus2, and sus4 chords. I know major chords are made up of the first, the third, and the fifth of the scale, and from memory I think that minor chords are the same as major chords, apart from the interval to the third is a minor third (hence the resultant chord has it's third of the scale one semitone flattened).

Suspended chords (sus2 and sus4) however are arousing a bit of confusion from my end. I can see that in sus2 chords the third is brought down to the second, and in sus4 chords that the third is brought up to the fourth. Presumably this would explain the '2' and '4' in the name - but that leaves me questioning the 'sus' portion of their name. I remember that intervals in scales and also be suspended (EDIT: Whoops! I remembered wrongly and was thinking of diminished, so I guess the intervals I talk of aren't anything to do with the chords after all, however my question of the origins still stands) or augmented, I however can't remember what makes an interval 'sus' or 'aug', hence I can't try and make a connection between these intervals and the 'sus' and 'aug' chords.

What's up with the 'sus' in the name of sus2 and sus4 chords? Is it simply as I'm describing and the 'sus' is just the way the names are, or does it have something to do with suspended intervals?

Answer 1

The 'sus' is short for 'suspended'.

The term comes from traditional music theory, and it refers to that the chord has a note that was suspended, or 'delayed', or 'carried over', from the previous chord. Traditionally the suspended fourth note in the sus4-chord should also be resolved to the third before any further chord action.

Example chord progression (with notes from bottom up including the bass line) illustrating a suspension with resolution:

F (F-A-C-F), Csus4 (C-G-C-F), C (C-G-C-E), F (F-A-C-F)

The top F of the first chord is suspended into the second chord, and then resolved in the third chord before we go ahead with the fourth chord. (If you ignore the bottom bass note you will find that the chords in the example are in inversions.)

However in many modern music styles the "suspended" note does not need to be prepared from the previous chord, nor does it have to be resolved. Thus sus chords have become chords in their own right, not depending on its surroundings. In this modern context the term 'suspended' might seem odd.

Answer 2

Scales can't have steps suspended; they can be diminished or augmented. Every step in a scale - hence also a chord - can be either of those. An augmented chord is two major thirds, a diminished chord is two minor thirds.

Sus means that you make a suspension by introducing a tension note.

Sus2 and 4 chords differ from the usual chords by thirds in that they are essentially chords by fourth. Take the note G and go a fourth up to C and another fourth up to F. Essentially you have the outline of a G7sus4 but that's not the point. If you put the G up an octave you have a Csus4. Put the C up an octave and you get Fsus2.