Heptachord analysis ??

[drb967]

A few years ago while in a theory class one of my professors "touched" on heptachord analysis / heptachord shifts primarily citing Bach's works. Just curious if anyone can offer any information about this topic beyond what I was taught. Simplified version I was taught was alteration of the melodic/ harmonic lines to effectively change (locally modulate-locally meaning inside a measure) the "local" key breifly.

[stevel]

Originally Posted by drb967

A few years ago while in a theory class one of my professors "touched" on heptachord analysis / heptachord shifts primarily citing Bach's works. Just curious if anyone can offer any information about this topic beyond what I was taught. Simplified version I was taught was alteration of the melodic/ harmonic lines to effectively change (locally modulate-locally meaning inside a measure) the "local" key breifly.

I'm not sure if I'm getting your meaning Rodney.

Hexachords are very important in Fugal writing, of which Bach was a particular proponent.

I've never heard anyone use the word "heptachord" for tonal music pieces other than as a "academic" form of the word "scale" (or key).

Bach's music, such as his Chorales, do in fact point at different keys almost measure-by-measure. These are not necessarily true modulations, and they are often too detailed to be considered tonicizations. In my experience, most people would call them something like "forays into the key area of III" or "a nod to the dominant key", etc. It is true that such shifts are brought on by melodic and/or harmonic alterations.

One good example is the way many chorales begin:
i - V/III - III (dm - C7 - F). It seems odd to start in D minor for example and modulate to F almost immediately, remain in F for a bit but then cadence in D minor. It's utterly baffling to many who analyze Classical homophonic pieces like Mozart where the modulations are usually pretty clear cut (not that there aren't not so clear ones!).

Is this anything like what you're asking about?

Best,
Steve

[drb967]

Yes this is what I am referring to - and he probably did refer to it as hexachord (my bad it was several years ago), as I recall he gave a listing of some of the more common "shifts." Will dig back through my notes to see if I can locate what he talked about (was only touched on for one day- but it seemed an interesting compostional 'tool' that I have thought to play with. Just thought there might be someone here with that "niche" of knowledge also.

[stevel]

Originally Posted by drb967

Yes this is what I am referring to - and he probably did refer to it as hexachord (my bad it was several years ago), as I recall he gave a listing of some of the more common "shifts." Will dig back through my notes to see if I can locate what he talked about (was only touched on for one day- but it seemed an interesting compostional 'tool' that I have thought to play with. Just thought there might be someone here with that "niche" of knowledge also.

The concept of hexachords being important in Fugue and other contrapuntal forms dates back to the hexachordal system in which there were three hexachords - natural, soft and hard. These equate to C D E F G A; F G A Bb C D, and G A B C D E. If you notice, they all are the first six notes of a major scale.

The "shifts" you're referring to might be what was called hexachoral "mutation". In other words, if someone wanted to sing E F G A B C, they'd need to begin with the natural hexachord and "mutate" (shift) to the hard (durum) hexachord.

By the way, hard or durum (also "square") has a B natural, and soft or molle (also "round") has Bb. This is how we get our names for the flat a natural signs - notice a natural is "squared" with hard corners, and a flat symbol is "rounded" with soft corners. This is why in German, "h" is B natural - the "h" is the squared symbol, and "b" is B-flat.

In fugal writing, the answer answers on the dominant. It is much easier to answer the Tonic subject with the Dominant answer if they contain similar interval structure. If one uses the natural and hard hexachords, one has 6 notes on the Tonic that can be transposed exactly up to the Dominant key area (without having to worry about that pesky F# in the key of G!).

I would Google "hexachord mutation" and "hexachord fugue subject" and see what you get.

Best,
Steve