Common Tones

Finding a set of guide tone lines for a specific set of changes (chord progression) is not the exact science we music theory geeks would like it to be. It is possible – even probable – for one to discover multiple sets of guide tone lines for a particular tune.

One good way to get started is to listen for “common tones” – in other words, pitches that are contained in two or more adjacent harmonic structures. The classic example is the plagal, or “Amen” cadence, in which a IV chord moves to the tonic I chord . For example, in the key of C, this would be an F chord resolving to C). In this particular case, the common tone is C.

 

When dealing with simple triads (three-note chords), these common tones are limited  to one pitch class  when a  major chord is followed by another major chord . For example, in the “perfect” cadence – the V-I (which is pretty much the basis of all Western tonal music) – the common tone in our example key of C would be G.

However, while G and F (the V and the IV chords) have tones in common with the tonic of C, they have no tones in common with each other.

Interestingly, as harmonies get more complex, common tones become more abundant. If we add a seventh to that V chord – so, in our example, make it a G7 – then the IV chord of F and the G7 wind up with a common tone, in this case, F.

By the way, in most “legit” music – particularly music composed between 1600 and 1820 – it is highly unusual (almost unheard of) for a V7 chord to be followed by a IV chord. However, it is common in jazz progressions, particularly those based on the blues. This brings us to the extended harmonies that have been an integral part of jazz music since the late 1930s.

If we add a harmonic extension, adding a ninth to that F IV chord, suddenly all three of our chords – C, F and G – have a common tone, which in our example would be G.

This harmonic sequence is of course the final three chords of the blues progression. Over a simple C lues progression in which an F9 is used, you could play or sing nothing more than a G throughout the entire form and it would sound fine – if a bit monotonous.

Returning to triads for a moment, it should be mentioned that when a major triad is followed by its relative minor – for example, C – Am – there are actually two common pitches. Do you know which ones?

The next step in discovering guide tone lines is to identify neighboring tones, which I’ll discuss in the next post.

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About GuideToneLines

KJ McElrath earned his Masters degree in Music Theory and Composition from Central Washington University. Composer of several works for big band, wind ensemble and orchestra, which can be heard at BardicCircle.com. I perform a cabaret act with Athena McElrath as McElrath Cabaret, which you can find at http://mcelrathcabaret.com.
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