I'd like to know if the following description is accurate: "A composer modulates from one key to another by the use of the “punning” chord, the augmented sixth (punning because it is also a dominant seventh)". Also, does he mean "punning" as "having two different meanings"? A bit of context: the speaker is Anthony Burgess, the writer (who also was a musician and a composer).
Great question; this is a particularly clever part of music theory!
Here's a nice little example in F major; it's just a
I--V7--I progression with a little cadential six-four thrown in there just because.
Meanwhile, this next example is in E minor, and it's a little bit different. It actually starts with what we call a
German augmented sixth, which then resolves to its own dominant and tonic.
I put a star above one chord in each example; it's above the
V7 in the F example, and it's above the
Ger+6 in the E example. You'll notice that they're actually the same chord! There are only three real differences:
- It's spelled with a
Bfin F major but with an
Bfin F resolves down while the
A#in E resolves up.
Ein the F example resolves up, though it resolves down in the E example (and eventually returns back to itself).
This means that we can be moving along in F major, get to a
V7 chord, and just conceptualize that
Bf as actually being an
A#, and we can just all of a sudden modulate down a half step! This is shown at the end of the second measure below:
So by a "punning" chord, you're exactly right: it's a musical pun because this starred chord, although it sounds the same, can function in two different ways. Others call it a "harmonic sleight of hand."
It's kind of like this joke:
Two fish are sitting in a tank, and one fish looks to the other and says, "Hey man, how do you drive this thing?!"
This works because "tank" has two meanings here; when we see it alongside the word "fish," we think it's a fish tank. Only later do we realize which version of "tank" is actually meant, and of course that's the joke.
It's the same thing here; When we first hear beat 4 of that last example, our brains assume it's just a
V7 in F. Only when we hear what comes next do we realize what was actually going on!
Note that this is also sometimes called a "common chord modulation," so named because the same chord is "in common" between these two keys.
When a chord contains the tritone - the augmented 4th that is the functional "engine" of a dominant 7th chord, we can exploit the symmetrical nature of this interval. "Punning" is a nice description of this!
Thinking in C major - the important part of G7, the dominant 7th chord of that key, is the tritone interval F - B, which tends to a resolution on E - C. But F - B may be respelled as E# - B, part of C#7, the dominant 7th of F# major!
When Beethoven explored methods of development through modulation, a favourite chord was the diminished 7th. C#, E, G, Bb. There are FOUR tritones in there, each one of which may resolve in two different directions! Oh joy!
It would not be a vast exaggeration to sum up all of Common Practice harmonic analysis as "hunt the tritone".