[Passing chords and the related subject of unessential notes in general are treated in detail in the book. The purpose of these blogs is to try and achieve a deeper insight into problems that usually appear in the A – Z of music-writing.]
Jazz and ‘dance band’ arrangers of old were obsessed with voicing styles and substitute chords. Many writers of the time felt that success lay in the skilful use of such features as, sometimes, it did. In fact, effective arrangements often use fairly orthodox treatments. It’s just the happy coincidence of all elements that ‘clicks’ with the listener. It’s also possible to write effective arrangements in which the rhythm or percussion instruments steal the limelight.
Nevertheless, the concept of ‘passing chords’ became an important feature of voicing styles for instrumental sections and ensembles. And it is important; I’m not saying otherwise. But there’s no simple formula for success. From the simple harmony exercises we all learn about early in our studies to the rapid flurries of strings and woodwinds used in more ‘advanced’ arranging different criteria have to be met.
Very slow ballades in the jazz environment will frequently feature a chord change on every beat or even under each note of melody, in which case there won’t be any ‘passing chords’ as such, whereas up-tempo music is characterized by simpler, more streamlined harmonies. Rapid chord changes have the effect of slowing the music down. (The basic chord sequence of the old standard ‘Limehouse Blues’ has a chord change every four bars for most of its duration.)
Inexperienced arrangers first encounter difficulties where there are two or more notes of melody to each chord. Decisions then have to be made regarding whether to designate a note to be either chordal or non-chordal and, to add to the problem, smoother voice leading can sometimes be achieved by treating a chordal note as being non-chordal.
Part of this process involves identifying the nature of ‘unessential notes’ – a useful term from ‘straight’ harmony I still use a lot. Jazz musicians tend to call all unessential notes ‘passing’ notes, regardless of their function but there are many types.
Another decision that has to be made is whether or not to allow reiterated notes in the voicing. This, again, is tempo-related. The more rapid the music becomes, the more important it is to write in a way that allows all voices to (approximately) follow the contours of the lead voice or melody. Slow the music down and the requirement for harmonic fullness takes priority.
Most of the time passing chords function as ‘chord changes within chord changes’ where harmonies used to voice passing chords will retain their conventional interrelationships. Whereas the chord sequence of a composition will have a rudimentary rhythm of its own, chords tending to change, say, on the bar or half-bar, the voicing of a melodic line will involve chords of shorter duration which are designed in such a way that the result doesn’t undermine the underlying harmonic sequence of the piece. So, basically, it’s the same thing over a shorter time-span. I’m tempted to say ‘only the time element has changed’ but that isn’t strictly true; as mobility increases, the need for smoothness in the parts increases, too. It’s all basic physics, really. Bodies moving at great speed can’t accommodate all the nooks and crannies they encounter.
Usually, passing chords will be chosen that use a minimum of notes that are foreign to the key. Where this can’t be done the diminished chord will always save us (this is because any diminished chord can be used as the starting point to modulate into any other key, both major and minor). In the context of good old four part ‘block’ harmony, we’ll use the diminished seventh chord in which, as everyone knows, the seventh appears in the guise of the sixth of the chord. (It’s already minor so if we flatten it again it becomes diminished.) The use of diminished chords in this way is especially successful in minor keys.
Where the lead voice or melody moves semitonally, all voices may move in exact parallel, particularly at fast speeds. This doesn’t prevent us from using a more conventional passing chord that permits the same semitone movement in the melody. The result may be stronger.
An interesting situation involves voicing a lead-in or ‘run-up’. These phrases are often harmonically un-motivated. The method is to write the last chord in such a way that it moves smoothly into the first bar of the following section of the piece, using an appropriate chord ‘shape’ (open or close harmony) and then to work backwards in each voice, following the contour of the lead voice but using only notes of the prevailing tonality, without considering the type of chord that results in each vertical ‘cross-section’ of the music. Other methods will seem clumsy, especially as the tempo goes up. Sometimes, a lead-in will anticipate the tonality of the approaching bar, especially in an ‘abrupt’ modulation. More adventurous arrangers can use such a voiced run-up over the top of sustained chords that are bringing the existing passage to a close. The clash will be tolerated by musically aware listeners and the ‘coming together’ at the end of it all creates a powerful tension and release effect. In music, we’re only concerned with where we’re going, which is the source of the surprise element.
As stated above, effective arrangements can be written using very simple effects. We don’t have to use every trick in the book. Nevertheless, in heavily-scored ensembles, the ability to combine sections skilfully is very important. Having said that, a powerfully written ‘bottom end’ involving middle and low pitched instruments will tolerate many apparent ‘transgressions’ aided by the difference in tone colour of the various instrumental parts. Passing chords in the upper parts are accommodated fairly easily by the simpler forms lower down. There is always a physical correspondence in nature and, in this context, it feels right for the lighter, upper parts to enjoy more freedom.