“Is parallel motion between two voices OK?”
I often get asked this question in class. Typically, a student has been told by a teacher that parallel fifths are bad. They’re often a bit indignant about it, as they like and want to use parallel fifths in their own compositions.
The following is my two cents on the topic. If you wish to skip the details… The main point will be, “If you want two parts to be perceived as independent voices, then parallel motion is bad. If you want two parts to be perceived as a single voice, then parallel motion is fine.”
(Disclaimer: this post is my opinion. So if you’re taking a music theory test, don’t assume that your teacher will agree with my point of view.)
My point of view comes from the following logic…
- First, what does parallel motion accomplish?
The answer is that parallel motion reduces the independence of two voices.
Let’s suppose you have two melodic lines that exist simultaneously. One is an ascending C major scale. The other is a descending C major scale. In this case, there is no parallel motion between the voices. They are two independent voices, and the listener would perceive them as two separate musical ideas.
In a different scenario… Let’s suppose you have two simultaneous melodic lines. The first is an ascending C major scale that begins on middle C. The second is an ascending C major scale that begins an octave higher. In this case, the scale is performed in parallel octaves, but the listener would perceive them as a single idea—an ascending C major scale.
In these and all cases, parallel motion reduces the independence of the two voices in question. In the first case, we have no parallel motion and the listener perceives two voices. In the second case, we have parallel octaves and the listener perceives a single voice.
- Second, why does the “parallel fifths are bad” rule exist?
The rule originated in music where the independence of voices was very important. In a four-part fugue, the independence of the voices gives the music forward momentum and direction. The voices fight against each other, building and building, until that tension is resolved at the end with a cadence.
Parallel motion in the middle of such a fugue would weaken the counterpoint and lessen the building tension. This contradicts the very point of the musical idea.
- Last, what are we to learn from “the rule”?
If independence between two voices is valuable in a given musical context, then parallel motion between those voices should be avoided. However, if for some reason the composer wishes the two voices to be perceived as a single musical idea, then parallel motion is not a problem.
Situation 1 – A 4-Part Fugue
The very point of a fugue is to build tension using four independent voices. If, somewhere in the fugue, you have parallel octaves or parallel fifths between two of the voices, then you have reduced the independence of those voices. You would end up with a 3-part fugue at that moment.
That would be a definite problem. Fugues depend on keeping those voices independent to create forward momentum and direction. The independence of the voices creates rhythmic and contrapuntal tension as the piece progresses.
Situation 2 – A Melodic Doubling
Let’s suppose you are writing an orchestral piece. You put a melody in the clarinet, and you double it up an octave with a flute. Essentially, this is “parallel octaves”.
Is it a problem?
In such a situation, you want the two voices to be perceived as a single idea by the listener. You don’t want the audience to perceive a melody and a countermelody. You want them to perceive a single melody, played by clarinet and flute.
Since you want the two voices to be perceived as a single idea, parallel motion is perfectly fine.
Situation 3 – A Melody and a Countermelody
Let’s suppose you are writing a film score love theme. You have a sweeping melody in the violins and a countermelody in the horns. Likely, you have some harmony parts in the low strings, low brass and low woodwinds. For a couple of beats in the middle of a phrase, you have the violin melody and the horn countermelody move in parallel fifths.
Is this a problem?
In this case, you want the voices to be independent. Here, you want the listener to perceive a three-layered texture—melody in the violins, countermelody in the horns, and harmony in the low strings/brass/woodwinds. When you use parallel motion between the horns and the violins, you fall back to a two-layered texture, which would be undesirable in the middle of a phrase.
Situation 4 – A Climax following a Contrapuntal Build
Let’s suppose you are composing an orchestral piece in 4-part counterpoint. The independent lines are creating a lot of tension, fighting against one another with different rhythms and contours. You’re enhancing the building tension by adding instrumentation, bringing in percussion rolls and brass. At the end of the phrase, you arrive at a huge climax. Here, you come out to a ƒƒƒ full orchestra statement using parallel octaves.
Is this a problem?
The act of going from four contrapuntal lines to a single melodic line can be very dramatic. This is particularly useful at the climax of a piece or at the end of a contrapuntal section. In this case, you are using the reduction in voices for a musical effect—to cap a climax. At such a climax you would want the listener to perceive a single musical idea and parallel motion is not a problem.
(Of course, had you used parallel octaves a couple of measures earlier—where the contrapuntal lines were being used to build tension—that would be a problem.)
Situation 5 – Background Keyboard Part
Let’s suppose you are the keyboard player in a rock band. There is also a drummer, a bass player, a guitarist and some vocalists completing the ensemble. You want to go from a vi chord to a IV chord. You do so, using some parallel fifths in all of their glory.
Is this a problem?
In this situation, I’d argue that the listener perceives the keyboard part as a single entity—background chords in the keyboard. In such a case, parallel motion is fine.
The key points are:
1) Parallel motion between two voices reduces the independence of those two voices.
2) If the effectiveness of the musical idea depends on those two voices remaining independent, then avoid using parallel motion.
3) If you intend for the two voices to be perceived as a single idea by the listener, then parallel motion is not a problem.
4) If you are in a music theory class, it is a common rule that parallel fifths/octaves should never be used. So implement point #3 at your own discretion (and probably not in music theory/harmony classes).