# Devil's Interval



## spaivxx (Oct 27, 2008)

I have posted this on some other sites. I have a ton more lessons of this nature so if any of you like this and would like more I will post more. There are a ton of lessons on how to sweep arpeggios, play ii-V7-I progressions, etc... all over the net so when I write I tend to focus more on the theory side of things, with a dose of history and background information. 

Here is a little about Tritones.

The devils interval, or tritone is one of the driving forces in western music. It was forbidden in Gregorian chant and even through the Baroque and into the Classical era one does not hear it often used melodically. Prior to the Baroque era, music "proper" was "harmonized" mainly with octaves and 5ths, and eventually 6ths and 3rds, all considered consonant intervals. I put harmonized in quotes because doubling a voice at the 5th or octave is hardly any real harmonization. 

However, harmonically, going back to the Baroque and onward, it is a different story. Without the tritone, the "dominant effect" would not be possible, not at least in the way it has been employed over the last 400 years. 

In any major or minor key, you employ a V7 (or variant there of) to create tension that begs to be resolved by the I chord. Keeping it simple, let's look at G7 to C. G7 employs the tritone B to F. B to F resolves to the major 3rd C to E. BF to CE makes a nice V7 I cadence. The B and F, being the two most important notes in the V7 chord, are heard as G7, even when the root and 5th of the G7 are not present, it's 3rd and 7th, the BF, imply dominant tonality. 

The tritone, on top of setting up the tension of an unstable and dissonant interval, sets us up for resolution by half step in two voices to the tonic. Half step resolution is smooth and strong. B resolves to C and F to E. On top of all that, the resolution sets up perfect contrary motion between the voices; a must in counterpoint music (such as most Baroque music). 

Bach, the preeminent composer of the Baroque era, used the tritone in this way in every single work that he ever wrote. Bach was primarily a church musicain, so it is cool and ironic to find him being among the first generation to grasp the power of the devils interval and unleash it upon the world where it would dominate harmony for over 400 years!!!! You will not find a Baroque work in which tritones were not used to this effect. Nor will you hear a Classical, Romantic or even modern work that is void of tritones, unless written employing some non standard harmonic system (and their are a few such as serialism or quartal harmony) . Tritones are in use in this fashion to this day. 

Another cool thing about tritones is that there are only a few of them the exist, so each has to pull double duty in another key. The B to F that we have been discussing is also working as F to Cb in the key of Gb. If one ever wanted to stroll from the key of C to the key of Gb, the tritone can show you the way. If that is not enough, the tritone is also borrowed by the parallel minor key to set up cadences, because the minor V heas no tritone. So instead of seeing Em7-Am in a cadence, we would see E7 to Am. This need to give the minor V a tritone is the origin of the *Harmonic Minor* scale. The need to correct the melodic tritone created when building melodies from the harmonic minor scale resulted in the birth of the *Melodic Minor* scale, in which both the 6th and 7th are raised, thus filling the augmented 2nd gap created by raising the 7 in Harmonic Minor. 

There is also the popular practice of _tritone substitution;_ basically any dominant chord may be replaced by the dominant chord a tritone from it's root. In the key of C, this would make Dm7-G7-C6 into Dm7-Db7-C6. You get a nice descending chromatic bassline outta the deal with the second one. 

So you see, a single interval holds the key to the energy which fuels our entire harmonic system. Perhaps for that reason alone it should be called the devils interval.


----------



## Mr. Big Noodles (Oct 27, 2008)

Cool read. Is there any chance that you could elaborate on tritone substitution?


----------



## spaivxx (Oct 27, 2008)

SchecterWhore said:


> Cool read. Is there any chance that you could elaborate on tritone substitution?


 
Sure, here is some detailed info. This is another repost from my archives. 


You can substitute any V7 chord with a diminished chord built on it's 3rd. Actually, this works so well that nobody will realize you did it, because the diminished 5th in the diminished chord is precisely what gives the dominant chord it's effect. Half step resolutions are smooth and effective, and resolving from a diminished 5th is really pleasing. 
Here is an example. G7 = G,B,D,F and Bdim = B,D,F,Ab 


The BDF are obviously common between both chords. Resolving either chord to a C major will yield plesing results. The diminished 7th will sound like a flat 9 to the listener, who is non the wiser that you just substituted the diminished chord. This is not a real change in harmony at all. The b9 also resolves well to the major 7th if the C were a C major 7. 
It also is the diminished 5th which allows the practice of "flat 5 substitution", which is a favorite device of mine. I use it in my chamber compositions and even in my symphonic works. 

It works basicly like this: 

You've got this chord: G,B,D,F = G7, heading to a C Major. The B-F = diminished 5th. F-Cb is also a diminished 5th. Cb = B. Since it is this tritone that defines the function of the dominant chord, changing a couple other notes in the chord will not drastically alter it's function. So, what chord contains the F-Cb tritine? You guessed it, Db7, the V of Gb. So G7 to C = Db7 to C. And, this Db7 to C is actually a smoother resolution than the original because it is full of nice half step resolutions, especially in the bass, say in a Dm7-G7-C (typical iim7-V7-I). Dm7-Db7-C (usually in a progression like this, CMajor7, CMajor6 or even Cminor7 works better than plain old C Major. Try dm7-Db7-C6 and dm7-Db7-Cminor7 and listen to the new meaning the progression takes on when you play with either of these chords.) Notice the chromatic movementin the bass of the progression when flat 5 substitution is employed. chromatic moving line in the bass....sweeet.. 
Flat Five substitution also works the other way. In other words, Db7 in the key of Gb may be replaced by G7 from the key of C. This is just the reverse of the above scenario. The progression in Gb, borrowing the G7 from C, looks like this: Abm7-G7-Gb. Remembering that we can resolve Am7-G7 to either GbMajor (or one of it's many variants), or GbMinor, suddenly the possibilites expand greatly for the use of a single Dominant 7 chord! 

Now that we grasp the concept of tritone interchangeability, it is easy to see how Dominant 7 chords may share the same pivotal role in modulation schemes as Diminished chords do. (discussed next). Since a lot of phrases, actually a great deal many phrases in almost every genre of music, use the Dominant 7 chord (or an altered variant) in phrase cadences, the Flat Five principle offers a very colorful solution to modulation between phrases or even sections of a work. The melody introducing the modulation need not altered drastically 
Diminished chords, strongly related to dominant 7 chords by way of the tritone,are used often to initiate modulation or serve as a dominant in a phrase cadence. This is where the diminished chord gets really fun. B,D,F,Ab = D,F,Ab,Cb = F,Ab,Cb,Ebb = Ab,Cb,Ebb,Gbb. These 4 diminished chords are all the same notes, the name is defined by their function. Moving a chord containing these tones to a C would make it a B dim, but resolving the same set of notes to E makes them Ddim, etc........ 

There are truely only 3 sets of diminished chords, one of which is discussed above. To find them all, play a diminished chord on the fretboard. Move it up a fret, that will yield the next set. Move up one more fret, that yields the third set. Go one more fret up, you have the same notes you started with!!! (Though in a different order). 

I don't need to say much here to get you thinking, with all these intercangeable diminished chords, the harmonic possibilites are endless!!! So much fun to be had with carefully constructed progressions that take advantage of the multiple personalities of these chords!!!!


----------

