I sung in a Gregorian Choir for a while(ome of those churchy habits we never got rid of,in Italy...),and I can clearly remember,by reading the scores,(by the way,the three types of writing music used for gregorian are so much more complete when it comes down to voice!!)the total absence of a scale...no tonics,no ways back to the first note,no sense of gravity.

Debussy's scale wasn't muddy,just suspended.He used exatonal scales,where there is a tone interval between note and note.It takes off those comfortable points like the sensible,the dominant,and so on.He used to say something like "the architecture is there,but don't you go looking for the pillars holding it:i got rid of them".But a lot of European folk music was already liberated from the gravity point,leaving it all to the feeling and not to the prettiness.

And by the way,I've always been told the contrary about Bach.I was told he approached music like a matematician,calculating cause-effect in his passages and such.He tought music,wrote it down,then would come the execution.Music that not only was beautiful to hear and to play,but even to look at.Ever noticed haw cute a score from Bach looks like?!I can hardly believe it an improvisation.Especially after playing it(I was going trough one of his suites today,wondering how long it took him to combine certain balances on the staff),I hear in Bach a very cerebral project,not an improvisation!!!But he's a decomposed composer now and who knows how his music was written,if it was improvised or not....