Chords by Thirds
The first chord constructions we will be looking at are the chords stacked by thirds. These chord formations must be one of the most commonly used and, in their simplest form, they are called triads. A triad is a three-note chord that is defined by its root, the relative 3rd and 5th intervals. If you consider the root of the chord as being C, the first third interval on top of it will be an E and the next third interval built on top of E will be a G.
The main chord types we can find are Major, Minor, Augmented and Diminished chords. Each of these is built with a root, 3rd and 5th intervals, the only difference being is that the quality of the stacked thirds changes, inside their respective triad. The first 3rd interval from the root of the chord is what defines its quality as being major or minor, while the 5th, when combined with a major or minor chord, will contribute the augmented or diminished quality of that chord. The main triads are built as follows:
As with scales, consider these intervals’ relative distance as the building blocks for every other chord of the same quality but based on different roots.
The suspended chords are also chords with three notes and they have the root, the 5th, but no 3rd degree because it was “suspended”, or moved, either to the 2nd or 4th degree of that particular chord. Because the 3rd is suspended, now the major or minor quality of the chord disappears as well, leaving us with sus2 or sus4 chords with either diminished, perfect or augmented 5ths:
The quality of the 2nd or the 4th interval in suspended chords may change as well, according to the chord’s root position in that specific scale or mode. For instance, if a sus2 chord is built on the 7th degree of the C major scale, we get the notes B C and F – root, minor 2nd and diminished 5th.
Tetrads or Seventh Chords
As seen, triads are three note chords but we also find tetrads, or four note chords, which are also very common. These are usually referred to as 7th chords and in order to build a 7th chord, you just have to stack another 3rd interval on top of the 5th of the chord. If you consider C as root, then the following intervals up to the 7th will spell C E G and B – being B the relative 7th of C:
There are three kinds of 7th interval associated to the main chord types; the major, the minor and the diminished. The following table shows how it can be related to the main chord types:
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