Subsidiary chord

In music and musical analysis, a subsidiary chord is an elaboration of a principal harmonic chord in a chord progression.

Tonic and tonic parallel in C major: CM and Am chords Play^ⓘ.

If the principal chord (X) is partially replaced by the subsidiary (Y), there are three possible positions - beginning, middle, and end - for the subsidiary:[1]

X–Ya

Y–X

X–Y–X

Modulation with subsidiary chord (in blue).[2] Play^ⓘ

For example, a subsidiary chord in a modulation.

A subsidiary chord may be a chord with related function and/or sharing pitches, for example in E major, C♯m (C♯-E-G♯) as a subsidiary for E (E-G♯-B), which share two of three pitches and are related as tonic parallel (vi) and tonic (I).