Theory Rules

[NLewis]

I'm wondering if anyone can tell me (hopefully in a detailed way) the actual reason that the following harmony rules exist:

1. No parallel fifths or octaves
2. No more than a 6th above the upper three voice parts

If anyone can think of more "rules", please also say them and explain "why" they are against the "rules".

Thanks!

[KGill]

1. No parallel fifths or octaves

During the medieval era, originally of course there was only one line in any musical composition; then they began to embellish this by doubling every note at the octave and also the fifth; eventually someone thought to provide further embellishment by having the voices not always moving exactly together (i.e., not homophonic but now polyphonic). In the later medieval era (starting probably around the 1100s) counterpoint was very basic and the voices were allowed to move either in parallel (with any consonant interval) or apart. With the Renaissance, though, polyphonic music became the required standard and this is why parallel fifths and octaves are disallowed in that era of counterpoint: it destroys the sense of having different voices. If you have two voices moving together in octaves, then really it's just monophonic with an octave doubling. Parallel fifths were thought to produce the same effect. Parallels in other intervals were probably OK because in strict counterpoint you are usually required to form complete triads and frankly it's almost impossible to write something without any parallels in it (assuming multiple voices). In the basic 'Renaissance style' the harmonious nature of the upper voices (which are free to move in parallel thirds, fourths, and sixths - this is assuming greater than three-part voicing) also tends to disguise the 'open' or 'medieval' sound that fifths and octaves would produce anyway. I'm not sure that aspect can be discounted in the prohibition either, to be honest.

2. No more than a 6th above the upper three voice parts

Sorry, what do you mean exactly?

[steltz]

I didn't really understand the parallels rule until I heard some music that broke the rule. Orchestral musicians (of which I'm one) probably have the least intrinsic understanding of it because the different timbres we hear all the time automatically make it possible to hear which line is doing what no matter how it is written. But with voices -- especially all male or all female -- it is impossible to follow each line individually if they are moving in parallel octaves or 5th. And, of course, in polyphony it is essential to be able hear each line individually.

Your second rule is something I heard slightly differently -- it was not to put more than an octave between any of the upper three voices. This keeps the voices close enough that they still blend well and sound as one unit (even though the individual lines must still be heard polyphonically). The exception is that your bass line can be slightly more separated, and it will still sound good. But if you, for instance, write the tenor and bass voices keeping them a 3rd to a 6th apart, and then there is more than an octave, and then the soprano and alto parts are within a 3rd to a 6th, it will sound more like two separate choirs. There is something of the unity that gets lost.

By the way, someone once did a study of Bach chorales and counted how many times he broke the rules. A bit silly, I think, but in each case there was another problem and the broken rule was the "lesser of two evils." Just goes to show that even the big guys have to break rules sometimes . . .

I suppose the issue is how artistically you break them and whether you maintain the integrity of the whole.

[JSB]

The melodic minor scale has a raised 6th and 7th whilst ascending, lowered or naturalised while descending. One genenerally does not mix these up, ie ascending with the natural version, or descending with the raised. Also, one does not incorporate both simulateously. Bach and others followed this protocol rather extensively. This allows for the tendency of the semitone 7th to rise to the tonic, and the descending 6th to fall a semitone to the 5th. There is merit in understanding the available chords that come from this procedure and its effect on establishing key centres. Of course one can mix them up, but there is value in hearing the purity and inherent strenght of the harmonys basic delineations. Also the melodic line tends to follow passage right through to the tonic or 5th depending on direction without moving away from the sequence, ie E - F# - D.. One would write E-F#-G#-A, in A minor. There are hundreds of rules aka guidelines, but its always for harmonic and melodic clarity. (Orchestration is a whole other system of far more rigid rules based on experience). Modern music tends to mix anything up with anything else, but bog standard harmony in its simplest form with basic modulations will always be the strongest, even in terms up pure physics. ie the relationship of tones within a pentatonic scale relating to the simplest and strongest series of harmonic relationships. Techniques for managing the sytem is the reason for the rules. How to introduce a key clearly and unambiguously, then modulate with clarity. Once understood, more caricatured or animated techiniques can be employed whilst mainting mindfullness of the inherent harmonic strenght or gravity of the principles of the overtone series, which ultimately governs everything.