Music in four-part harmony, for four voices of different pitch, has been written since the sixteenth century.  When I was at school, I was required to write music according to the rules. It made composing very hard work, and I always felt I was creeping through an obstacle course trying to avoid all the pitfalls.  There are so many things you have to avoid. Parallel fifths and octaves, doubling the leading note, and omitting the third are all capital crimes. “Unsuitable leaps” are also a no-no.  

These rules of harmony, as I understand it, were developed in the 1800s based on the work of Johann Sebastian Bach, who had already been dead for over 50 years.  Let’s make this clear: Bach wrote sublime music, and he did not write any rules for other people to follow.  The rules were reverse-engineered. People who like rules and instructions dissected his work and from it extracted patterns which shaped the lovely harmonies he created.  These have been fossilised as “the rules for harmony” ever since.  This is an interesting sentence from a current A-level textbook:

Overlaps (where the bass leaps higher than the tenor’s last note) and part-crossing (when, for instance, the tenor sings higher than the alto) are best avoided, although they were used fairly frequently by Bach. 

This makes it explicit: Bach did not follow the rules of harmonising like Bach. 

Generations of musicians have now learnt to harmonise in the style of Bach. Examinations – both A Levels and practical Associated Board exams – still require this rigorous exercise. 

Nowadays I love writing and arranging in four-part harmony. The big difference is that I am writing something to be sung, and it is not going to be marked.  The official rules are in my head, but I choose not to follow them.

My priority must be that the song is singable, which has two factors to it.  First of all, each part must be in a comfortable range for the person singing it – not too low, and not too high.  My community choir singers are not professionals and we don’t like squeaky voices, so the top note for the soprano line is five or six notes lower than you would find in Bach’s choral works.

If the soprano does not go very high, and the bass does not go very low, we will be left with plenty of potential for voices overlapping. All our tenor singers are female, so the alto and tenor lines are in much the same range. If they don’t overlap, they end up very monotonous.    

This leads us to the other aspect of singability: a singable line has to feel good in the mouth and appeal to the ear. The notes must move up and down, otherwise it’s boring and difficult to learn. When the voice jumps from note to note, it should not be too surprising. I’ve taught a couple of songs with awkward jumps and often people leave them out, make up something they like better, or sing that section very loudly to show they’ve got it right and throw the balance off.  There are good reasons, then, for avoiding “unsuitable leaps”.

Sometimes, though, when I’ve written a section and played it back, it doesn’t sound quite right. That’s when it’s worth dusting off the rule-book – if I fix the crimes against Bach, it often sounds better!