Post your playing posers and technical teasers to: Theory Godmother, Guitar Techniques, 30 Monmouth Street, Bath, BA1 2BW; or email me at email@example.com - every wish is your Godmother’s command!
David Mead sorts out your musical malaises and creative conundrums.
Accept No Substitute Dear Theory Godmother
Please could you explain to me how tritone substitution works?
Derek Tritone substitution, or b5 substitution as it is also known, is one of the more confusing areas of music theory. When I was ploughing my way through theory books many years ago I read the basic rule that went something like: “You can substitute any chord which has the flat 5th of the original chord as its root”. All well and good, but it’s not strictly accurate or very clearly explained; furthermore, they don’t say why it works. So let’s look at why tritone substitution can be used in jazz and other related music styles.
The chord that lives at the heart of tritone substitution is the dominant 7th. The dominant 7th demands some sort of resolution, the most common of which is the V-I. The reason why this works is that every dominant chord has a dissonant b5 interval between its 3rd and 7th (Ex 1) and when this is followed by the I major, that dissonance is resolved. What happens in a V-I resolution in C major is that the G7th’s 3rd and 7th both shift by a semitone to form the C’s major 3rd, the most consonant interval in music (Ex 2). So what you’re hearing is the movement between a dissonant (tense) interval to a very consonant (settled) one, hence the sensation that things have resolved and the music is now at rest.
Tritone substitution exploits the fact that a b5th can be looked at in two ways. In our example, the notes B and F moved a semitone each in opposite directions to form C and E, but what happens when we look at it upside down? That gives us F and B which just happen to form a b5th interval too. No other interval in music will do this, so if we look at the dominant chord that contains F as its 3rd and B (here referred to a ‘Cb’ because of the key signature) as its 7th, we find Db7 – a dominant chord exactly a b5th away from G. Db7 will resolve nicely into Gb major (Ex 3) but, because of the b5th or tritone in common between G7 and Db7, it will also ‘stand in’ for G7 and make a plausible substitute for it. Try comparing both in Ex 4 and you should hear that the resolution is sound in both cases.
To sum up, if you find a V-I resolution in a tune, it’s often true that you can substitute the V chord for a dominant a b5th away. There are more uses, too, but I think it’s best that you fully understand the basic concept before you move on to its more advanced applications.
Scaling The Blues Dear Theory Godmother
Could you tell me why the six-note minor Blues scale is considered to be minor Pentatonic with an additional note (b5th), and not a diatonic sevennote scale with one note subtracted?
Jakob I think the reason is because that’s how many guitarists come to the Blues scale in the first place, Jakob - they learn the minor Pentatonic and then find this extra ‘cool’ note to tack on. But you can’t view the Blues scale as a diatonic scale because the truth is there are no regular scales that contain three semitones in a row, as the Blues scale does (4-b5-5). If you took one note away from any diatonic scale you wouldn’t end up with the Blues scale at all.
Theoretically, the minor Pentatonic is the Natural minor scale with two notes missing (2nd and 6th), and the minor Blues scale simply adds the b5th as a passing note. But in practical terms for most guitarists it really is the minor Pentatonic with the b5th added.
(There’s also the major Blues scale, which is major Pentatonic with b3rd added, but we won’t go into that here, although Ex 6 shows Major and Minor scales beside their relative Pentatonic).
Getting back to minor Blues scale, if you factor in the blues ‘curl’ - the b3rd pushed slightly sharp or slightly ‘major’ - you get a scale that looks relatively simple on paper but which can cover a multitude of musical situations.
Many guitarists then add the full Major 3rd, and then the 6th and the 9th to create hybrid scales that are great for pretty sophisticated improvisations. And, as if by magic, turn to page 16 and Jon Bishop will explain this very concept in glorious Technicolor!
Locomotive Breath Dear Theory Godmother
I love playing Every Breath You Take by the Police ( Guitar Techniques Dec 2014), not just for the great tune but also as an exercise in strict timing, arpeggio technique and palm muting. But no matter how much I work on my fretting hand I cannot do the stretches from static chord positions. So I end up racing up and down the neck fingering every note separately. Is there some other solution?
Colin The span of the hand does improve with practice, Colin, and this tune is a good workout in order to bring it about. The only tip I can pass on here is one that Andy Summers himself told me, which is that he uses his first fretting hand’s finger to play both the bass note and the major 3rd in the tricky Aadd9 chord (and likewise for the b3rd in the F#m9) which actually makes it a lot easier to play and cuts down the stretch somewhat (Ex 6).
The only other thing I can advise you to try is to capo the neck around the 4th or 5th fret and practise the tune in a different key (with smaller fret stretches) until you nail the fingering, then drop the capo back a fret at a time until you’re playing it in the correct key. As I say, the span of your hand should increase over time and you should soon be perfecting your performance of the song - take it one breath at a time!