Harmony Hub

The Elements of Harmony > Quadriads (basic)

The Quadriad

The term "Quadriad" means 'a group of four different elements'. It is like a Triad with a fourth different note added to it. In order to achieve the greatest possible consonance with the other three notes of the chord, the fourth note must form an interval of a minor or major 7^th with the root, or 'fundamental' note. Although this interval is itself dissonant, the fourth note (called the 7^th) will form a mildly consonant interval of a major (or minor) third with the 5^thbelow, and a perfect consonant interval of a fifth with the 3^rd below (except in the dominant 7^th and minor/major 7^th Quadriads), thus rendering the chord more acceptable to the ear.

Stacking all combinations of major and minor 3^rd intervals, we obtain 6 Quadriads. Taking C as bass note, we have:

Major 7^th Quadriad	Has a major 3^rd interval between C & E, a minor 3^rd interval between E & G, and a major 3^rd interval between G & B.
Dominant 7^th Quadriad	Has a major 3^rd interval between C & E, a minor 3^rd interval between E & G, and a minor 3^rd interval between G & Bb.
Minor 7^th Quadriad	Has a minor 3^rd interval between C & Eb, a major 3^rd interval between Eb & G, and a minor 3^rd interval between G & Bb.
Minor 7^th(b5) Quadriad	Has a minor 3^rd interval between C & Eb, a minor 3^rd interval between Eb & Gb, and a major 3^rd interval between Gb & Bb.
Minor/major 7^th Quadriad	Has a minor 3^rd interval between C & Eb, a major 3^rd interval between Eb & G, and a major 3^rd interval between G & B.
Major 7^th(aug) Quadriad	Has a major 3^rd interval between C & E, a major 3^rd interval between E & G#, and a minor 3^rd interval between G# & B.

While all these Quadriads are intrinsically dissonant, we can assign them a degree of dissonance, based on how few or how many of the dissonant intervals are present between all their note pairs . The dissonant intervals are the minor/major 2^nd, the augmented 4^th, or the minor/major 7^th. See Intervals (basic).