So, we've been looking at reharmonization for awhile. Let's continue.
Because the tritone occurs only in the dominant chord, its presence defines a dominant chord. A tritone is a very unstable interval. It sounds as if it wants to go someplace, which is why V chords want very much to resolve (often to a I chord). If you play just the two notes of the tritone, they sound like a V chord, incomplete though the chord may be. What's so unusual about a tritone is that it's the 3rd and 7th of not just one, but two dominant 7th chords.
B and F, the 3rd and the 7th of G7, are the same notes as F and Cb, the 3rd and 7th of Db7. (B and Cb are enharmonic-the same notes, just spelled differently.) Because the tritone (the 3rd and 7th) of both G7 and Db7 is the same, G7 and Db7 can substitute for one another.
Quite often this tritone substitute V chord is preceded by its II chord, creating a II-V progression.
Here's the II-V-I in C
Here's the same II-V-I, but with Db7, the tritone substitute, replacing G7.
Here's Ab-7 preceding Db7
With Ab-7, Db7, the tritone substitute II-V, replacing D-7, G7:
The 3rd and 7th of a V chord always form the interval of a tritone, no matter which note is on top. Why? Because a tritone is exactly half an octave and if you invert it (put the top note on the bottom, or vice versa) it is still a tritone. The roots of the G7 and Db7 chords are also a tritone apart.
Another reason to play a tritone substitution is that it often makes the melody note more interesting. There are two reasons for playing tritone substitution on the melody of a tune:
* To create a chromatic bass line
* To make the melody note more interesting
I learned to play tritone substitution in blues. Hoping to cover this in the next post.
I have read the following quote many times and have heard this explanation on Jamal Hartwell's Tritone Xtravaganza and also you'll find the reference here:
"The Devil’s Interval, they called it when it was banned by the Church in times long past. Then someone realized it’s a really cool interval, and lifted the ban. Or something like that. Six semitones from the root, C-to-F#, this interval is found in a lot of heavier music.
The ascending tritone, otherwise known as the flat fifth (a name that just doesn’t have the same dramatic flair), can be associated with The Simpsons (The Simpsons – I’ve italicized the syllable where the tritone is sung) or Black Sabbath’s Black Sabbath.
Descending, the tritone can be associated with Jimi Hendrix’s Purple Haze or YYZ by Rush (if you can listen without getting distracted by their odd rhythm and timings)."
Right now Jermaine Griggs is having a sale with free shipping on the 300 pg. course book (that I have been talking about. You know, the theory book) and giving away for free Gospel Keys 101 (great Dvd for harmonizing the melody). You pay $52.00 Click here for more info Sale!
All the best,
"The beautiful thing about learning is that no one can take it away from you." B.B.King