On the screen, you can see the harmonic properties of the minor blues. The structure of the minor blues is characterized by the presence of traditional tonal progressions. For example, the translation of the subdominant in measure 4 uses an applied dominant seventh chord, or secondary dominant C7. And the motion to G7 in measure 10 is prepared by the flat 6 harmony. That chord, A flat 7 is one the notable exceptions to the otherwise normative root movement found in the basic blues progression. When you compare the root movement of the minor blues with that of the basic blues progression, you can hear that they are almost identical. With the exception of the chord built on flat 6, scale degree in measure 9. Let me play you a progression so you can hear this sound of the minor blues. 1, 2, 1, 2, 3, 4. [MUSIC] Okay, so we have a new chord. A flat 7 going to G flat 7. There are a couple of ways that we can explain the structure and the placement of that chord and its function. So, first one is to basically, this is like an upper neighbor of G7. Nice way of preparing and anticipating the structural harmony. [MUSIC] But there is a more interesting way of explaining the nature of that chord besides its upper neighbor relationship to the structural dominant 7. And it is to point out that its trident relationships to the chord build on scale degree 2. That normally occurs in that location. Remember, in measure 9 in a major blues we had the 2 chord moving to 5 chord. So in the minor blues in measure 9 we have an flat 7 chord, which is trident away from the D chord. That should've been there, but it's not. We can explain how that relationship works, and in order to do that we have to introduce very important concepts in jazz theory called tritone substitution. On the screen, you can see the three step process of explaining how does tritone substitution work. So first, the diatomic version of the two chord is changed to the dominant seventh chord. So let me explain what I mean. In our Mr. PC Progression, the two chord should have been D minor 7 flat 5, going to D7, going to C minor. And in measure 9 of the regular blues, that's what happens. G minor, C7 1, 2, 5, 1. So in minor blues, since we are in the minor key, we're going from minor 7 flat 5, going to dominant. So, first thing, we'll change the chord quality of the two chord from minor 7 flat 5 to dominant 7, to major. And that substitution is quite common at the predominant level and we've already encountered that substitution in other locations of the blues. For instance, the turnaround measures to 11 and 12. In F Major we have 3, 6, 2, 5. We have a minor 7 chord, minor 7 chord, minor 7 chord. We can easily substitute these minor chords with dominant chords [SOUND] without violating the rules of a voice leading. And jazz pianist and jazz guitar players frequently do these kind of substitutions, just to enhance their harmonic vocabulary and add some spark, harmonic spark in the revision. So first thing, going back to our Mr. PC Progression, we changed the quality of the predominant chord from minor 7th flat 5 to dominant 7th. The next thing, while keeping the guide tones of D7 in place, see what happens when we transfer the root up or down a tritone. Doesn't really matter, because tritone subdivides the octave into two parts, so it doesn't really matter where we go. So if you go up a tritone, we're going to go to A flat. New root. So when you listen to the sound of these two chords, dominant type of chord and A flat. They are both the same quality, but see what happens to the status of these guide tones. In the diatonic version, F sharp, the third becomes flat 7, and the seventh of D7 becomes the third. So it kind of reversal status. So the new harmonic root, redefines the quality and the status of guide tones, and that's really, really, really important. So you can see how we get from predominant diatonic version. Dominant change of quality to tritone sub. And that's our chord that happens in measure 9 of the minor blues. But the harmonic status, functional status of these two chords is exactly the same. It doesn't matter whether you play this. This is far more colorful I think, as opposed to- [MUSIC] And it's another advantage. Check out the voice leading between A flat and G flat. It's stepwise as opposed to moving by fifths. So the tritone substitution then has its theoretical origins in the symmetrical division of the octave. And in inversional invariance of the tritone. To summarize, the tritone between the guidetones is invariant, basically stays the same. And the roots of the diatonic and chromatic versions of the dominant seventh are tritone apart. In fact, any dominant 7th chord, diatonic, can be replaced by its tritone counterpart. Which in many cases enhances the overall harmonic progression. So for instance, leaving our blues discussion for a moment, it's a great standard tune called What's New. It starts with- [MUSIC] 5, 1, right? [MUSIC] So it sounds really good when you play the atonic version of that progression. [MUSIC] But if we replace the G7 with the tritone substitution, we're going to get a completely different and unique harmonic color. So compare the sound of the diatonic version of this gesture, 5 1 to a tritone substitution change. [MUSIC] Tritone sub, diatonic. [MUSIC] And tritone sub. [MUSIC] Okay, so there are in our minor blues, Mr. PC blues, there are three places where you can experiment with your tritone substitution. And on the screen you can see these three locations, and this new dominant 7th chords are written in red. So in measure 4, we have G flat 7. In measure 9, we have A flat 7, and in measure 10, we have D flat 7. Remember what happened in measure 4. In the original version, we had C7 chord. So the relationship between C and G flat, tritone apart, right? Same thing, we've talked about A flat 7, so you know what happens, it replaces D 7, but D flat 7 is a tritone sub of G 7. So now, when I play the progression with tritone substitution, it will sound completely different. So let me play it with the metronome, 1, 2, 1, 2, 3, 4. [MUSIC] And one more with that tonic version. [MUSIC]
