Today we’re going to talk about this chord:

Nowadays we see this chord as a subV/V, but in the Classical period this chord was treated using a very different perspective. Composers back then, saw this chord as an augmented sixth chord.

Although these two points of view are very different, the reason for using this chord was the same back then as it is now: to tonicize the V chord — in what we call: a Half Cadence.

For those of you studying tonal harmony, I think this will clarify how, and why, this chord works, and how to solve those challenging tonal Harmony worksheets that your teacher always seems to be giving you.

For jazz musicians this is just a subV/V. When you play it on the piano, it’s clearly a dominant chord. And there’s three variations: the German augmented sixth (with all of the regular notes), the Italian augmented sixth (which has no 5th), and the crazy French augmented sixth version (with a b5).

Now, in the classical era, they didn’t see this chord as a dominant chord — made out of the 1 3 5 and b7. Here’s how this chord works for the classical mind…

This concept was developed from the perspective of being in a minor key. It works perfectly fine in a major key, but the augmented sixth chord was conceived from the perspective of being in minor.

So let’s say we’re in the key of C minor.

What’s the V of C? G! Now, what is the best trick to tonicize that G? Well, if we use the Ab (only a half step above G), and an F# (which is the leading tone to G), when we write it down, we have an augmented sixth, which resolves to that G in octaves by contrary motion.

Remember this: the augmented six chord always resolves to the V of the key in octaves (or doubled unison, if we’re using an inversion of the augmented sixth chord).

But an augmented sixth is nothing else than a b7. Ab to F# is the same as Ab to Gb. If we now add the 3rd of the chord, we get an Ab7 dominant chord without the 5th. And this C wants to go to the 3rd of the G chord like this… This is the Italian augmented sixth chord.

If we also add the 5th of the chord (Eb) we get the German augmented sixth. And of course Eb wants to go to a D (the 5th of the G chord)

So now, we have a beautiful tension-release effect. These two notes resolve in contrary motion. By the way, in the Italian sixth we can double the 3rd of the chord — since we don’t have the Eb — and then, one C moves down to the B, and the other moves up to the D.

But what if the Eb is already resolved to the D? That’s the French augmented sixth.

The D is already present in the augmented sixth chord. It doesn’t have to move at all.

So now, when you see a problem like this…

…just think like this:

The Ab wants to move down a half step. So it goes to G, which must be the 5th of the key. And the G is the V in the key of C minor. So we’re in the key of C minor. We’re going to resolve the G’s in octaves. So the top note has to be a leading tone to G (F#). And there’s your augmented sixth (Ab to F#)

And we add the 3rd of the chord (C) which by the way, is always the tonic of the key that we’re in. And to make it a French augmented sixth, we have to add a D — which is the 5th of the G chord — already resolved in the chord. This D is actually the b5 of our Ab chord.

So once you understand the purpose of this chord, and how it works, it’s very easy to solve this problem.

Let’s do another one.

This Eb will move down to D. D is the V in our key, then we’re in the key of G minor. And the other D — an octave above — should be approached by its leading tone (C#)

Then we add the 3rd of the chord, which is our tonic, and since it says that it’s an Italian augmented sixth, we just double it. I’m going to go ahead and put it an octave higher in the upper voice. Now, one G moves down to F#, and the other moves up to A. A nice D chord.

Let’s do a German augmented sixth.

So, F has to move down to E, right? Then, E is the V of our key, which means we’re in A minor. Now we have to add the leading tone to E — which is D#. Now we add the 3rd (A) and the 5th (C). So this chord is the German augmented sixth in the key of A minor, and look: it’s an F7! It just looks weird when we write it down like this, and of course, it resolves to an E chord like this…

And remember, this is just a substitute of the V/V — on the opposite side of our circle. This German augmented sixth, in the key of A minor, is just an F7 that is replacing the B7 — the five of E.

I think it’s super interesting how harmony has its roots in counterpoint. Nowadays we would never write an F7 chord like this but, should we?

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