Why the dominant chord is unstable... but not that unstable
Ok. What do I mean by unstable? Well, you have to bear in mind that most music is culturally determined. In other words, the culture you grow up in
determines how you perceive music to a surprising degree. For example, I understand that Javanese gamelan funeral music, which in its own culture is
unbearably mournful, sounds rather jolly to us.
What does the foregoing have to do with the price of beans? Well, we're now at a stage in our musical culture where dissonance is far less frowned
upon than in previous eras. In fact, it's looked on as adding pleasant spice to the dish, rather than something to be used only very occasionally
and as part of a musical journey.
So, strictly speaking, a dominant seventh chord is supposed to be dissonant or tense. Musicians speak of tension and resolution: the dominant is
supposed to "resolve" or go somewhere. Hopefully you'll have started to notice that in the D7 to G progression we looked at in a previous post.
We are conditioned to think that the D7 sounds good before the G chord. The G chord is "where it's supposed to end up".
But for the past 60-odd years we've lived in a world where your basic 12-bar blues is based around a dominant chord, to the extent that we now speak
of "static" and "resolving" dominant chords in jazz. "Resolving" dominants are the ones with the crunchier notes in, for example the #5 and b9
But the thing that's at the heart of the dominant chord is the interval of a tritone
: that's what
makes dominant chords so special.
That Wiki article is really cool. Check out the "devil in music" part. The tritone was once regarded as so dissonant that it was the mark of Satan
himself. I don't know if you've ever seen the movie "Crossroads" (NOT the one with Britney, the one with the equally irritating Ralph Macchio)
but Steve Vai plays the Devil's guitarist - a part for which he's singularly suitable, I have to say - and he finishes off his first solo with a
massive tritone. Nice.
Here's how to play a simple 12-bar blues using tritones.
For this, we'll be using three chords, but we'll be stripping these down to just the tritone and taking everything else away. I'd love to have
found my old diagrams about this, but I think I've cleaned them off my computer and they're on a backup disc somewhere. Please bear with me.
For this we will be requiring three chords : A7, D7 and E7.
- thumb on bottom E at 5th fret
- first finger on D string at 5th fret
- third finger on G string at 6th fret
- second finger on A string at 5th fret
- first finger on D string at 4th fret
- third finger on G string at 5th fret
- second finger on A string at 7th fret
- first finger on D string at 6th fret
- third finger on G string at 7th fret
All strings not being played are muted with the fretting hand. To play the chords I'd recommend a pick-and-fingers approach.
So your 12-bar will go:
a7/// D7/// A7/// A7///
D7/// D7/// A7/// A7///
E7/// D7/// A7/// E7///
So if you're feeling courageous you can strip out the root of each chord and just play the notes held down by your first and third finger. Those are
the tritones at the heart of each dominant 7th chord.
Now as you may have gathered from the Wiki article (love that stuff about temperament btw, it's a really cool subject if you ever want to get into
it) the tritone is a symmetrical interval, it's exactly half an octave.
So let's look closely at what happens in those three chords. Hang on to your hats.
So the first chord, A7, has got G natural and C sharp on the D and G strings respectively. G is the flat seventh of the A chord, and C sharp is the
The second chord, D7, has got F sharp and C natural, but now they're inverted. The note on the D string, which was the flat seventh, is now the
third: and the note on the G string, which was the major third, is now the flat seventh.
That might take some time to fully get but it's really important.
[edit on 4-4-2009 by rich23]