Chord Formations – Triads and Tetrads

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 3^rd and 5^th 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, 3^rd and 5^th intervals, the only difference being is that the quality of the stacked thirds changes, inside their respective triad. The first 3^rd interval from the root of the chord is what defines its quality as being major or minor, while the 5^th, 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.

Suspended Chords

     The suspended chords are also chords with three notes and they have the root, the 5^th, but no 3^rd degree because it was “suspended”, or moved, either to the 2^nd or 4^th degree of that particular chord. Because the 3^rd 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 5^ths:

     The quality of the 2^nd or the 4^th 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 7^th degree of the C major scale, we get the notes B C and F – root, minor 2^nd and diminished 5^th.

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 7^th chords and in order to build a 7^th chord, you just have to stack another 3^rd interval on top of the 5^th of the chord. If you consider C as root, then the following intervals up to the 7^th will spell C E G and B – being B the relative 7^th of C:

     There are three kinds of 7^th 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: