source file: m1419.txt
Date: Mon, 18 May 98 18:29 BST-1

Subject: Re: tetrachords

From: gbreed@cix.compulink.co.uk (Graham Breed)

The impression I get is that tetrachords are _more_ common than the
diatonic scale.  I think of it as being related to octave invariance.
The octave is the most consonant non-trivial interval, and so scales
tend to repeat about it.  The most consonant intervals within an
octave are the perfect fourth and fifth, so there is usually some
repetition on that level as well.

That doesn't explain why Lydian and many Indian scales have sharpened
fourths up from the tonic, of course ...