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What To Know About Minor Blues and Tritone Substitutions



In this video, guitarist Patrick Arthur explains the Minor Blues form and provides an understanding of Tritone Substitutions.

The Minor Blues share the same 12-bar structure as the 3-chord blues from the previous video in this series but also has some key differences that set it apart. The “one” chord in this case is a minor 7 (also written as i-7). This translates to the 1 b3 5 b7 of a given scale. For example, the minor blues above is in the key of C minor so the first chord would contain the notes C Eb G Bb (the 1 b3 5 b7 in the key of C).

You will notice that the movement from i-7 to iv-7 stays consistent with the 3 chord blues we already discussed, again the only difference here is the chord quality. (These chords were dominant in the 3 chord blues). If we break this down into three 4 measure phrases the minor blues can be thought of as follows:

Phrase 1 = i-7 for one bar followed by iv-7 for one bar, then back to i-7 for 2 bars Phrase 2 = iv-7 for 2 bars, then back to i-7 for 2 bars Phrase 3 = bIV7 for one bar, V7 for one bar, i-7 for one bar, then a “turnaround” of bVI7 to V7 for 2 beats each. The turnaround typically only takes place when you repeat back to the beginning to play the melody or take additional solos. Otherwise, you would end on the i-7 chord.

Making sense of the bVI7:
Most of the chord motion and chord relationships in this blues should look familiar to you if you have already watched the previous video on the 3 chord blues. The only one that really stands out here is the bVI7 chord. In the above example, it is an Ab7. As a reminder, this chord is a dominant chord and the spelling is as follows – 1 3 5 b7 (in the key of Ab the notes would be Ab C Eb Gb).

This chord has a unique sound and function. The easy answer as to why this works is because our ear is typically ok with hearing half-step resolutions (the Ab7 resolves down a half step to G7, or the V7 chord). However, there is more going on under the surface that helps justify the use of this seemingly “strange” chord.

We talked about the V to I relationship in the previous video, in this case, the G7 wants to take us back to a C-7. The quality of the “One” chord doesn’t matter too much as long as the V chord is dominant. For example, a G7 could take us to a C7 in a standard 3-bar blues and by that same logic a G7 wants to take us to a C-7 in a minor blues (as it does in the above example).

We can also approach the V7 chord with the same resolution, something we call the V of V (also commonly called a secondary dominant). We don’t have to get bogged down with all these terms and names though, the important thing to understand is that any chord can be approached by its relative V7. So in this example, we are approaching a G7 (the V7 chord in our blues) with its relative V7. We just need to find what the 5th degree of a G scale is to do this.

Here’s our 1 3 5 b7 spelling of a G7 chord = G B D F. With this we can see that the 5th degree is a D. This means we can place a D7 chord in front of our G7 chord to achieve a V to 1 resolution.

Now let’s spell an Ab7 chord = Ab C Eb Gb. Both the D7 and Ab7 share the note C and the note Gb(F#). These notes are the 3rd and b7ths of their respective dominant chords. The 3rd and 7th of any chord are what I think of as the “chord descriptors,” meaning if we know the 3rd and the 7th then we know whether or not a chord is Major or Minor, or if it is a major 7th or dominant 7th. Since these 2 crucial notes are the same we are allowed to swap these chords for one another, making use of something called a “tritone substation.” A tritone is an interval of a #4 (or b5). If we count up 5 from a D major scale (D E F# G A) and lower the 5th note we get an Ab. So our Ab7 chord is really acting like a D7, making use of the V7 of V7 (or secondary dominant) relationship.

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