Voice crossing, in practice, is not forbidden, and actually is somewhat common. Voice crossing is where one voice, say the tenor, crosses above or below the adjacent voice. In the example below, the tenor crosses above the alto:
Voice crossing is not a musical crime. We see it all over the place in Bach chorales and other classic four-voice settings.The problem arises, however, when a voice crosses above the soprano, which, to the listener, changes the melody. The following example, a harmonization of the beginning of Frère Jacques, is somewhat extreme, but demonstrates my point. As far as the listener is concerned, the melody is completely destroyed because the alto moves higher than the soprano, thereby taking on the role of the melody:
Voice crossing also can be a problem when an inner voice moves lower than the bass, when it’s done unintentionally. But again, there is nothing wrong with voice crossing if the result is intended. But most of the time, for beginning music theory students, it is not intended. So many music theory books and teachers instruct students to avoid it altogether saying, “Don’t do it!”
Spacing limitations have to do with acoustics. Do you remember the harmonic series? The larger intervals are at the bottom, becoming progressively smaller moving up the series. So for the best sound in four-voice harmony, as a general rule, it’s best to have larger intervals near the bottom, smaller intervals near the top. We’re not real concerned about how much space there is between the bass and the tenor, because they’re the lowest two voices, although a limit of an octave plus a fifth (a 12th) is a good rule of thumb to follow. However,
- there should never be more than an octave between any two upper adjacent voices (SAT).
In other words, there should not be more than an octave between the soprano and alto, or between the alto and tenor. Again, composers sometimes do it for the effect. But for a good sounding four-voice harmony, adhere to this principle.
In four-voice harmony, voices ideally should have as much independence as possible. For this reason, certain intervals moving in parallel motion have been avoided in traditional tonal music. These are parallel octaves and unisons, and parallel perfect fifths. Why? Remember, we’re writing four-voice harmony. When two of the four voices move in parallel octaves or unisons, the effect is that of reducing four voices to three. Parallel fifths, while not as blatant, were avoided probably for the same reason, since they are so close to the fundamental of the harmonic series (3rd harmonic). In the examples below, I use “//” to indicate parallels:
We’ll conclude with one final type of forbidden motion: direct, sometimes call hidden motion. Again it involves octaves and fifths, but this time only the outer voices, that is, the soprano and the bass. Direct motion occurs when the soprano and the bass move in similar motion to notes that create an octave or a fifth between them. Direct motion is not allowed because it sounds like parallel fifths or octaves, even though it’s not. Direct motion should be the least of your worries since it’s not easy to do. Three conditions have to be met to have direct octaves or fifths:
- Direct octaves or fifths only occur between the bass and soprano.
- The soprano must move by leap (not step).
- Two different chords must be involved for direct octaves or fifths to occur.
All of these conditions are met in the following examples:
Final Word on the Forbidden Zone
Parallel octaves are very powerful, even in vocal music. Carl Orff used them to great effect in his choral masterpiece Carmina Burana. Parallel fifths are powerful as well. Rock music would not be rock music without parallel fifths!
So let me emphasize again, we are not disqualifying music that disregards principles of good voice leading. However, learning to write traditional four-voice harmonization is a valuable musical discipline that will deepen your understanding of all music!Print This Post
You’ve probably heard parts of Carmina Burana without knowing it. It has been used in commercials and in movie trailers (e.g., Mel Gibson’s Hamlet), It is an incredibly powerful piece for chorus and orchestra. And Orff breaks all the rules!. Do yourself a favor and download this 20th century classic: