Straight Line Chords: Aug, Dim, Sus2, Sus4
Major and minor chords look like triangles on the lattice. They are closed loops, which I think contributes to their stable feeling. Up a major third, up a minor third, and down a fifth (due West on the lattice) brings you right back where you started. The intervals interlock, and they are all consonant, reinforcing the sense of harmonic rest.
Other combinations of notes are more open. Many chords look like straight lines on the lattice.
These chords often show up in my animations as fleeting transitional harmonies. In Flying Dream, for an instant, there’s even a stack of three major thirds:
To my ear, this stack of thirds has a distinctive sound, almost like cloth ripping.
A Suspended Second chord is a straight line, like an augmented chord, but on the horizontal axis. It’s a stack of two fifths. At the time the Sus2 and Sus4 chords were named, the 2 and 4 were usually “suspended,” or held over from the previous chord, as a tension to be resolved. Now they are often used as full chords.
The Police used these stacks of fifths a lot. Andy Summers’ guitar part for Every Breath You Take is full of Sus2 chords, alternating with major and minor thirds.
To me, Sus2 feels lightly stable, and wistful. All the intervals are overtonal, and quite consonant, but unlike the major and minor triads, the Sus2 doesn’t come full circle. If it keeps going, it will never return home, but climb on up the endless spiral of fifths.
It’s a great way to end a certain sort of song, finished but with a sense of longing.
This chord has a wonderful tension. The root establishes home. The 5 is overtonal, stable, with strong tonal gravity that attracts. The 4 is reciprocal, unstable, with a strong tonal gravity that repels.
Resolving to the 3 is satisfying indeed, as the unstable 4 slides from its unstable peak into the stable gravity well of the major third.
Sus4 chords are all over rock music. Pinball Wizard is a study, here it is by Townshend on acoustic guitar: