> I'd be curious to know what makes one style of music more 'rational'
> than another. In what way is say a Haydn symphony more rational than a
> ricercar by Frescobaldi or a motet by Ockeghem?
Solving the pythagorean comma thingy? After that, the circle of fifths exactly chimes with the octaves, making modern harmony possible (because now you can modulate using the same instruments rather than needing to grab new ones).
I'm perfectly open to the idea that you can define rationality differently (and that sufficient unto every culture is the rationality unto). But I think what mostly matters here is the "sound of regularity" for Joanna, who has grown up in that system, and who seems attracted to music that sounds less regular by its criteria -- which unites middle eastern music with Renaissance motets.
Another ways to think of it are parts that seem (to the modern listener, socialized as we are) more independent and less subordinated to, and contrained by, the pattern of the whole.
Michael