mediants

Mediants are a concept in tonal music theory referring to the third scale degree of a diatonic scale. The mediant chord is the triad built on that degree, and the relationship between the tonic and mediant chords is known as a mediant relationship. In harmonic analysis, the mediant is often designated by the Roman numeral III.

In major keys, the diatonic mediant triad is typically a minor chord. For example, in C major, the mediant triad is E minor (E-G-B), so the key’s mediant is denoted III. The mediant relationship is frequently used to modulate or color harmony, providing a more distant contrast than the predominant and dominant functions.

In natural minor keys, the diatonic mediant triad tends to be major. For instance, in A minor, the mediant triad is C major (C-E-G). The exact quality of the mediant can vary with different minor-scale forms (natural, harmonic, melodic), which can yield augmented or diminished mediant sonorities in some contexts.

Chromatic mediants describe mediant relationships where the roots lie a third apart but the chords are not diatonic to the same key. Common examples include moving from C major to E major or to Eb major. These progressions are used for color and surprise, often sharing one or more common tones despite their non-diatonic roots.

Overall, mediants provide a flexible tool for harmonic color, modulation, and expressive contrast within tonal music.