Normally at the end of a phrase we find some type of cadence. If chord V (or V7) is used as the penultimate chord, the final chord of the phrase will usually be chord I, making a perfect cadence.

Occasionally though, other chords may be found in place of chord I, and the most likely would be chord vi.

The cadence V-vi (or V-VI in minor keys) is called an interrupted cadence. It normally sounds a little bit surprising, because our brains are conditioned to expect chord I after chord V. Composers can take advantage of this, and use it to extend a piece of music by first writing an interrupted cadence, then continuing for a little while longer, before the expected perfect cadence arrives.

This (edited) example is taken from Mozart’s Piano Sonata no.3, K281 (2nd movement).

interrupted cadence V-VI in Mozart

In SATB (four-part harmony) the third of the chord is doubled in chord VI, when this cadence occurs in a minor key. This is to avoid breaking other rules of harmony.

SATB doubling interrupted cadence

Here is another example, from Bach’s Chorale no.196. Interrupted cadences are relatively rare in Bach Chorales.

interrupted cadence