re: Tetrachords R Us

>>Here's a question which I was originally going to post privately to
>>Chalmers,I've read about them for
>>many years, and all of a sudden I realized that I don't know the
>>fundamental reason behind their origin. Any thoughts are surely
>>appreciated....thanks...Hstick

Neil: - I was waiting for John's succinct response myself, but I'll
throw in that tetras operate as three-interval sets below an initial
tone. Then began being joined as pairs, with a 'diazeuksis' separating,
ending up with octave closure. That's how I think of tetrachords.
John's articles and book are much more informed. Joscelyn Godwin
also expresses their origins and simplicity very well in "harmonies
of heaven and earth"