Principles of Part Writing

The music of the common practice period did not appear overnight. The principles that govern it were the result of almost 1000 years of scientific research and artistic experimentation. One of the principles is that of equal emphasis on both harmony (vertical) and line (horizontal). The process of writing music that addresses both of these aspects is referred to as voice leading or part writing (these two terms are used interchangeably). Four-part choral music is most often used to demonstrate and teach voice leading, since it addresses most of the problems, methods, and principles for writing for more or fewer voices. Four voice choral part writing is often referred to as SATB (Soprano, Alto, Tenor, Bass) part writing. Although all parts follow the smooth, melodic principles discussed in the previous section on melody, the issue of contour is usually reserved for the soprano alone.

Ranges

The following are the ranges allowed by most theorists for each voice. Although it is certainly possible for good singers to sing beautifully beyond these ranges, it is helpful to have a rather fixed limit for each voices range to effectively study this craft.

When writing parts, it is important to always keep each voice within its range, and also not to allow voices crossing (when a higher voice becomes lower than a lower voice). Voice crossing blurs the distinction between the parts, especially when played on a keyboard instrument. The following is an example of voice crossing. Notice how when the voices cross in this example, the first two beats will sound as though the alto and tenor repeat the same pitches.

Voice overlap is when a line crosses above or below a pitch recently sounded by another voice. Although this is not voice crossing, when the notes are only one to three beats apart, the ear may still hear the voices as overlapping, and the independence of line is diminished. Although Bach and many other great composers occasionally wrote overlapping parts, there was always a good, melodic reason. So, unless there is a compelling compositional reason, this error should also be avoided.

Types of Motion

By definition, two or more voices can move in only four basic types of motion:

1) Parallel Motion - both voices move in the same direction by exactly the same interval. In this example, both voices move down by a M2.




2) Similar Motion - when both voices move in the same direction, but by different intervals. In the following example, the top voice moves up by a M2, while the lower voice moves up by a P5.




3) Contrary Motion - the voices move by any interval in the opposite direction.




4) Oblique motion - one voice moves in any direction by any interval while the other remains on the same pitch, not moving at all.

Part Writing Procedures

In order to achieve a level of independence of line for all four parts, parallel motion of Perfect Octaves, Perfect Fifths, and Unisons should be avoided. Since these are the lowest intervals on the overtone series, when two or more voices move in parallel motion in these intervals, they can blur together and sound like only one voice (in the case of unisons, they actually become one voice). Parallel motion by thirds, fourths and sixths is acceptable and often desirable, however, two voices should not move in parallel motion for several beats in succession. This would reduce their independence. To most easily avoid part writing errors, the following procedure is very helpful:

1. Begin with a good melody using the principles discussed in the section on melody. Use a general contour that is in contrary motion to the bass and try to keep the melody and bass lines at least an octave or more apart.When they become too close together, you can create a bottleneck/jam that usually results in part writing problems. Be sure all tendency tones resolve properly and avoid all parallel fifths and octaves.
2. After you have a good melody, move forward writing the inner voices one chord at a time.
3. Stay within the ranges of the voices. If you notice that a voice is getting toward the limit of its range, try to move inward if possible. Also, Keep the space between each of the upper voices (all except bass) within one octave or less (i.e. Soprano to Alto and Alto to Tenor spacings are each an octave or less).
4. Use only notes that are a part of the harmony. Non-Chord Tones will be discussed later. If it helps, lightly dot in all pitches belonging to the chord between the melody and the bass so you know what choices are available.
5. Keep common tones when possible in your inner voices. Often there may be a pitch that is a part of adjacent chords. Since parallel motion is to be avoided, avoiding motion of a voice all together eliminates that possibility.
6. When you must move, move the inner voices in contrary motion to the bass by the smallest interval whenever possible. This one simple step eliminates most part writing errors.
7. The 7/7 rule: scale degree seven (the leading tone) should resolve to tonic (always when in an outer voice, unless a part of a line proceeding down from tonic to dominant, (i.e.: 1-7-6-5)) and the seventh of a chord should always resolve down by second. Neither of these should be doubled.
8. Don't double any note with a chromatic alteration and resolve chromatically altered notes by step (the interval of a second) in the direction of their alteration. For example, an added flat lowers the pitch, so it should resolve down by step. Added sharps raise the pitch, and should resolve up by step.
9. Finally, check each voice for undesirable parallel motion between each of the other voices. Recheck the ranges for voice crossing and overlap. Be consistent and systematic in this. Just as good drivers look twice before crossing an intersection, good part writing students double check their work before moving to the next chord.

When problems arise:

1. When you find yourself erasing a note or chord 2-3 times, stop. There is a problem. First, check to be sure all of your notes fit the specified chords. Wrong notes usually lead to voice leading problems. Be sure also to check backwards one or two chords for errors.
2. Back up one or two chords to a point where you have another choice in how the chord is voiced or arranged. Try rearranging the pitches in a manner that doesn't form new problems (i.e. voice crossing, voice overlap, exceeded ranges, etc.) then try moving ahead with the inner voices on their new paths.
3. If problems still arise, you may need to rewrite the melody, beginning back 2-3 chords. If this happens, try opening up the spacing between the melody and bass even more to allow more options for the inner voices.
4. Large leaps (more than a third or fourth) often cause voice leading problems. If you see a large leap within one or two chords of your problem area, go back and rewrite the part so as to reduce or avoid the leap.

Doubling

When writing triads, there are only three pitch classes but four voices. This means that two or more voices will have the same pitch class. This is called doubling. When you have a choice, try to double the root or fifth of the chord. Avoid doubling any note with an accidental added or a tendency tone.

If you follow these basic steps, most part writing errors may be avoided. As rigid as they may seem, you often will have several choices yet available. The following example demonstrates these principles:

Links:

• Next Section: Non-Chord Tones
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