Species Counterpoint (part 2 – Rules of Polyphonic Motion)

        Before studying the specific rules of each species of counterpoint, there are some basic principles of polyphonic motion that we should understand.  The first concept among these principals is the fact that there are three types of polyphonic motion.  They are direct motion, contrary motion and oblique motion. 

        Direct motion consists of two or more parts moving in the same direction (ascending or descending) by step or skip.  Whether the parts move in equivalent intervals (all steps, all skips, equal distances) is irrelevant.  The only relevant factor to qualify polyphonic motion as direct is that the parts move in the same direction. 

  

      Contrary motion consists of two parts moving in opposite directions (ascending and descending) by step or skip.  Again the interval of movement is irrelevant since the classification of contrary motion is only contingent on the direction of the motion.  This type of polyphonic motion can only occur between two parts since there are only two directions of motion (ascending or descending).  A third part would have to duplicate one of these two types of motion, and thus be an example of direct motion with that part. 

        Oblique motion consists of one part moving (by step or skip) while the other part remains stationary.  The stationary part could be a single pitch with a rhythmic value that is longer than the pitches of the moving part, or it could be repeated rhythmic occurrences of the same pitch.  As we will discuss in future lessons, the rhythmic value of a piece of counterpoint may vary from that of the cantus firmus only in certain species. 

        Now that we understand the three possible types of polyphonic motion, we can discuss the four fundamental rules of polyphonic motion.  They are listed below:

1. From one perfect consonance to another perfect consonance one must proceed in contrary or oblique motion.
2. From a perfect consonance to an imperfect consonance one may proceed in any of the three motions.
3. From an imperfect consonance to a perfect consonance on must proceed in contrary or oblique motion.
4. From one imperfect consonance to another imperfect consonance one may proceed in any of the three motions.

These four rules can be boiled down to two basic principles.  When we are traveling to an imperfect consonance, we may use any type of polyphonic motion.  However, when we are traveling to a perfect consonance, we must avoid direct motion.      

        As a result of these rules, composers find it more desirable to utilize imperfect consonances in their polyphonic writing.  This results in less restriction on the types of motion that they can employ.  In addition, imperfect consonances are perceived to be more harmonious than perfect consonances.  The pure quality of perfect consonances cause them to sound hollow or empty.  The impure quality of imperfect consonances cause them to sound rich and full.    Therefore, the majority of harmonic consonances within a polyphonic work should be imperfect otherwise the work will seem to lack harmony. 

       However, a work of counterpoint must start and end with a perfect harmonic consonance in relation to the cantus firmus.  To be more specific, all works of counterpoint must end with either a unison or octave.  In addition, any work of counterpoint that is composed below the cantus firmus must begin with a unison or octave.  Works of counterpoint composed above the cantus firmus may also begin with a fifth. 

This cannot be done with counterpoint that is composed below the cantus firmus because a fifth below would result in an obscuring of the perceived key.  Another rule of polyphonic motion is that all counterpoint must remain in the same key as the cantus firmus.  A starting interval that is a fifth below the cantus firmus could be perceived as a Do – Sol relationship in which the counterpoint is starting on the tonic even though it is actually a Fa – Do relationship in which the cantus firmus is starting on the tonic.  This dilemma could obscure the perceived key of the polyphonic work, and is thus avoided. 

The perfect fourth is considered to be a consonant interval when examining two pitches outside of any other musical context.  Remember, the perfect fourth is an inversion of the perfect fifth, and is thus heard as a similar interval.  However, within various musical contexts the state of this interval is more complex.  The best way to understand consonance and dissonance in polyphonic music is to think of consonant intervals as stable in relation to the key, and dissonant intervals as unstable in relation to the key.  Therefore, any interval of a fourth that requires resolution is considered to be dissonant. 

Since the perfect fourth is and inversion of the perfect fifth, Do – Fa relationships can easily be misperceived as Sol – Do relationships (as discussed earlier).  Any polyphonic situation that obscures the identity of the key would be considered dissonant, and in need of resolution.  In works containing three or more voices, additional pitches may help to support the integrity of the key and cause an interval of a perfect fourth to be considered consonant.  However, in two part compositions the perceived dissonance of the perfect fourth would be unavoidable. 

Now that we have an understanding of the basic principles of polyphonic motion, we are better prepared to discuss the specific rules of each species of counterpoint.  In future lessons on each species, please review the principles of this lesson.  Once we apply these principles through the practice of polyphonic composition, they will become easier to understand and retain.   

       
         This Learning Music With Ray video gives an overview of the basic rules of polyphonic motion that govern all polyphonic composition. After gaining an understanding of these rules, one will be better prepared to study the specific rules of each species of counterpoint. The video starts by discussing the three types of polyphonic motion. I then cover the four fundamental rules of polyphonic motion. Next, I discuss the difference between perfect and imperfect consonance in polyphonic music. Finally, I go on to discuss other miscellaneous rules of polyphonic motion, and the dissonant nature of the perfect 4th in polyphonic music.