Eight-Part Vocal Writing: Basic Theory

Recently I began writing a piece, a setting of the Guardian Angel Prayer (Angele Dei) in the original Latin. Because of the full and lush harmony that can be achieved, as well as the abundant opportunities for using color tones, I concluded that eight-part writing would best suit the setting I had in mind for this prayer. However, as some of you may know, there are no set rules specific to eight-part writing. Here I will expand upon my own findings and methods.

First, the theoretical rules that are common with four-part voice leading:

No movement in parallel fifths

No movement in parallel fifths by contrary motion.

No direct fifths, that is, movement in two voices to a perfect fifth by similar motion, except if one voice (usually the higher) moves by a step.

No movement in parallel fourths with the bass.

This is permitted with the soprano or melody line, though it should be avoided.

Attempt contrary motion as much as possible. * (see next paragraph)

Attempt not to double the leading tone.

This will result in parallel octaves that would not be recommended (more on parallel octaves below).

However, one of the leading tones may jump down to the fifth (in rare cases, the sixth), thus avoiding unpleasing parallel octaves, though this motion may sound just as clumsy.

Do not overlap voices (one voice sings the exact same pitch another voice sang immediately before).

Overlap also occurs if one voice sings a note lower than the next lowest voice sang previously, or higher than the next highest voice sang previously. This type of overlap is acceptable in certain cases.

Do not cross parts.

This should be even more strongly avoided in eight-parting writing.

It is more desirable to enter into unison and then back out again rather than crossing lines.

Avoid continuously repeated movement of thirds and sixths (more than several times between the same two voices).

Spacing is not an issue, considering that the harmonies will be very tight to begin with. Contrary motion in eight-part writing will be more than your best ally. It is very, very easy to lapse into prohibited parallel motion with so many voices being involved.

Now for the modified rules (according to my practice) that apply to eight-part voice leading:

Parallel octaves should be avoided but are permitted under these conditions:

A voice does not move in parallel octaves with the soprano (or melody line).

A voice does not move in parallel octaves with the bass.

A voice can only move in parallel octaves with another for ONE movement of notes.

Only ONE pair of voices out of the eight can move in parallel octaves per movement of notes.

The leading tone, as explained above, should be avoided for a candidate for parallel octaves. It will sound unpleasing and cause the composer to use a clumsy route to avoid them.

Unisons are permissible under these conditions:

Two voices do not move in unison under any circumstance (remember, we are writing for eight voices, and we should keep to such as much as possible).

There is no more than one unison per "chord," unless:

Melodic and/or harmonic reasoning override this.

The composer wishes to transition down to six, five, or four voices, etc.

As for distribution of chord tones throughout the eight voices, the chord should be as balanced as possible. However, since the harmony is so dense, there is much more leeway in what can be doubled, tripled, or even quadrupled in some cases. When writing in eight voices, let the melodic line determine the distribution of chord tones, and do not be afraid to experiment with unbalanced structures. Sometimes the desired sonority must be achieved by an unbalanced method.

These eight-part theoretical rules are practices that I have found to work. However, they are not set in stone, and another person may find different rules that work just as well, or better. I would greatly appreciate input on this post.