(musth1) The Submediant Chord

Yes, this is a one-chord-only post.

The submediant (vi, VI) chord has three usages: as a tonic prolongation, as a deceptive resolution, and as a predominant chord.

The submediant as tonic prolongation

The submediant can be used after a tonic chord as part of a common falling 3rd progression. It almost always leads to a subdominant class chord.

RN:     I – vi – ii6 – V – I
Class: T – T – S  –  D – T

RN:     I – vi – IV – I (or I6)
Class: T – T – S  –  T

For both progressions, tonic is prolonged by the following of the submediant triad (through the shared chord tones of 1 and 3). For the second progression, the entire four-chord sequence can be analyzed as a tonic prolongation.

The submediant as substitution for tonic (deceptive resolution)

When vi follows V or V7 instead of I, the listener hears the “substitution” of the vi as a deceptive resolution. Some important things should be kept in mind.

• If the resolution happens at a cadence, we call the progression a Deceptive Cadence (DC). We only call it a deceptive cadence if it happens at a cadence.
• If it occurs anywhere else in the phrase, we call it a deceptive resolution, or deceptive progression.

V to vi almost always occurs in root position, and this is how we’ll handle it in our part-writing examples. Since the progression is an ascending second root movement, the general advice of upper voices moving in contrary motion to the bass is followed except for one important caveat: You must resolve the leading tone to tonic. Move the other two voices in contrary motion to the nearest chord tones, which will result in a doubled third (scale degree 1) of the submediant chord.

The submediant as a predominant chord

vi can move directly to V, functioning as a predominant chord. This type of function happens much more rarely than the above two functions, as it is a descending second progression. We see this type of movement more in the Romantic period. When you part-write this progression, you have to be careful not to write objectionable parallels, or end up with a doubled leading tone in the dominant harmony.