Is there a name for this kind of prolonged tension?

Question

There's this song I really like, with a fairly long and elaborate chord scheme in a major key (probably C, but I'm not too sure). The last two lines of the chord scheme sound very common, however:

|IV  |V   |vi  |vi
|IV  |V   |I   |I

Now, since IV-V-I progressions are extremely common, the vi chord is fairly unexpected in this location. To me it seems like it resolves the tension created by the V chord, but only partially, since everybody expects that chord to be resolved to I instead.

Subsequently, the IV-V buildup is repeated, and finally does resolve to the expected I chord. By first resolving to an unexpected chord and then repeating the first two bars of that line, I feel like the iv chord helps to create a prolonged tension that is eventually resolved with the I chord.

Does this make sense at all? I haven't seen this pattern very often in other music, but I find it quite fascinating and it works very well for me. I think there might be a name (and an explanation) for this kind of chord progression, so I thought I'd check whether anyone on music.SO knows about it. :)

Answer 1

The resolution V to vi is called deceptive cadence. In C major this would indeed be G => Am, and in C minor you would get (maybe even more convincingly) G => Ab. The vi chord (or VI in minor) replaces the tonic and it usually contains the expected melody note but replaces the expected harmony (the tonic chord). This is possible because the vi (or VI) chord shares two of the three chord tones of the tonic chord.

This device is quite common in classical music as well as in popular music. Also relatively common is the more general idea of harmonizing an expected melody note with an unexpected harmony. E.g., at a point where the root of a piece is expected to be harmonized by the tonic chord (at some supposedly final point), it can be harmonized by the IV chord, or - mainly in a jazz context - by a bIImaj7 chord. An example for the latter is a Dbmaj7 chord replacing a C chord (in C major) with C as a melody note (which is the major 7th of the Dbmaj7 chord).