Triad

What it means

A triad consists of three notes stacked in thirds: root, third, and fifth. It has been the basic building block of Western harmony since the sixteenth century. Depending on whether the two thirds are major or minor, four kinds result.

Musical use

The major triad has a major third below and a minor third above; the fifth is perfect. The minor triad has the reverse order, minor below, major above, likewise with a perfect fifth. In figured-bass notation, a triad in root position is usually not designated at all. Only major and minor triads count as consonant; the other two contain a dissonance and demand continuation.

On the degrees of a major scale there stand, within the scale, three major triads, three minor triads, and one diminished triad. The principal functions tonic (I), subdominant (IV), and dominant (V) are major triads; the secondary degrees carry minor sonorities and count in functional theory as their substitutes.

A triad can appear in three positions: in root position with the root in the bass, as a first-inversion chord with the third in the bass, as a second-inversion chord with the fifth in the bass. It keeps its name in the process; only weight and sound change. Which note lies on top determines the position in the narrower sense and is independent of this.

In four-part writing one of the three notes must be doubled; in root position this is as a rule the root.

The triad is the basic unit of tonal harmony. Historically the triad was described as an independent unit only in the sixteenth and seventeenth centuries, for instance by Gioseffo Zarlino and Johannes Lippius. In functional theory the principal triads carry the functions tonic, subdominant, and dominant.

Performance practice

Practise triads in all positions and inversions and listen to how their weight shifts. Intonate the third with care — low in major, high in minor. And impress the four kinds on your ear; distinguishing major from minor is the most profitable single ear-training exercise.