Well, we've taken a look at the Neapolitan sixth chord and let's move on now to the augmented sixth chord, and note that, well, I guess the first thing I'll say is the way, at least at this stage, to... the best way to think about the augmented sixth chord as a chord of substitution is that it substitutes for a four chord in first inversion. Let's... let me, let me show you how to, basically, from the four chord create an augmented sixth chord. And through that we'll actually talk about why it's called an augmented sixth chord. But first let me play this progression so you have it in your ear. A few videos ago, I spoke about the Phrygian Half Cadence, and where there's a cadence, this is a perfect example of a Phrygian Half Cadence, where we go forth and first inversion to five. So I just want to, while we're talking about this chord, I want to suggest that, in fact, this is one of the ways that we can set up a Phrygian Half Cadence with the either fourth and first inversion or the augmented sixth chord. Okay, so in order to make an augmented sixth chord, here's our root before we... what do we do? We lower the root, right? We lower the root to get the Neapolitans. What we're going to do here, in fact, is just raise the root. Like this. Let me play these two next to each other, so you can hear the difference. So one would usually describe this augmented sixth chord as being maybe more colorful than, than this one. I guess that's kind of a personal taste, but this is certainly you could imagine being a kind of surprise if you had a section that was largely diatonic and, all of a sudden, you get this chord it would be fairly striking. What I want us to know about now, though, is where does this name of augmented sixth come from? And to do that I want to just throw in this root note. This is the same note here as D-flat and if we look at it, we see that when this chord is in first inversion and this is the bass note, actually, to be honest, the augmented sixth chords do not have inversions. We always see this note that is the sixth scale degree. The sixth scale degree is always viewed as the root note or the bass, the note that should appear in the bass. Even though what it yields is a chord that looks like some kind of first inversion chord. But the name augmented sixth simply comes from this, when you raise this to get the sound of the augmented sixth, you cause an augmented sixth interval to occur between this lowered sixth scale degree and this raised fourth scale degree. And that's where the name comes from. Now, to be clear I should add in something, though. And that's this. There are, well, there are three, there are actually four types of augmented sixth chords and I'll talk about three of them. This one is called an Italian augmented sixth, so now, sorry, now I can actually do the harmonic analysis. We have one and we get... Let me get this Italian. Italian augmented sixth to five. This is the Italian augmented sixth. If we... so and how we describe it? Well, we've got a third here, you know, and then we get the augmented sixth. Notice we have three notes, three notes in this augmented sixth chord and they're characterized by the third above the bass and the augmented sixth above the bass. Let's do a different version. To do this version we only need to change one note. There, and we're going to call this... the German augmented sixth chord. So we have Italian, we have German, and so how do we describe this? Whell, this has four notes in it. It's got a root, here's your third. Here's the fifth above the bass, or... sorry, we should go back, bass note, third above the bass, fifth above the bass, and augmented sixth above the bass. Now, if we look at this, we can also see that, well, it's spelled differently, it actually sounds like a dominant seventh chord. An augmented sixth is a different spelling of the same sound as a minor seventh. And then we have here this bass note, third above it, fifth above it. And these three notes form a major triad. So this actually sounds like a dominant seventh chord, but it does not function like a dominant seventh chord. Okay. And then the final one... that I want to talk about... Hopefully this doesn't switch over. Good. Is called the French. The French augmented sixth chord. And it's spelled like this and it's characterized by... here's your bass note, here's the third above that bass note, here's the fourth above it. And note this is an augmented fourth. And then this augmented sixth above the bass. Let's hear how these sound and, then, what I want to do is actually go back and talk a little bit about voice leading of this. So they all sound slightly different from each other. Did you notice my parallel fits here? So this is a good place to do the same thing we did with the new parts and chord. Oh, now it switches. Okay, good. Let's go down here. This is a great place to use a cadential sixth-four chord. It allows us to carry over this fifth and then resolve it down, so we don't get any parallel fifths and we get this very nice sound of a parallel sixth moving downward together. Well, that's one issue about voice leading these chords we need, but that's that's an old issue, right? I mean, we know that we need to worry about parallel fifths. The main thing you need to understand about voice leading any kind of augmented sixth chord is the following: This lower sixth scale degree, that's the bass of the augmented sixth chord, It needs to resolve down by semi-tone to the fifth scale degree. This raised fourth scale degree, which is the augmented sixth away from this, away from the bass, that needs to resolve upwards, that needs to resolve upwards to the fifth scale degree. So, if we abstract this a little bit, we just look at those... notes. We see if we get the augmented sixth and they move outward into an octave. This is really an important feature of this. It's also the reason why this does not function like, like a dominant seventh chord. I want to point that, go back, you know this German augmented sixth. This here. Now, if this has to go up there and this has to go down here, and this was, say, a dominant seventh chord, it would be the dominant seventh of G flat. So we can't get a G flat if both of these G flat major chord or a minor chord, if we've got to go to this C, it won't work. If it was really a dominant seventh chord, we would spell it like this, and then we'd find our leading tone, which is right here. This F. And we resolve it, the proper way to the tonic, and we find our fourth scale degree, which is right here, and we resolve it. And...this would go where it needs to go, and it's not ideal but...like that. I play this last one, this last measure. Something like that. Oh, no! That's awful! Look at this. This is fits by country motion. Well, I guess we have to do this. But if we respell this. If we spell this as an augmented sixth chord, we see this has to go out, this has to go out. Keep it coming tones. We get a one six four and then we get the five. The resolution to the five chord. Well, that last bit was a bit theoretical, I hope it didn't scare you off, but for those who are familiar with this kind of stuff I wanted to explain, and are feeling very comfortable with this, I wanted to explain why a chord that sounds the same as the dominant seventh chord, but it's spelled differently, does not function like a dominant seventh chord and it very much comes down to how that chord is spelled. How we spell chords in classical music really influences how we voice lead them and how they function.
