No angel, I'm entering this discussion midstream, having missed its
beginning, really w/ more a question than a statement of position.

I don't know the difference, if any, between dodecaphonic and 12-tone and
simply atonal music, and at this point I don't care.

I do know that Arnold Schoenberg devised a system for composition that
followed a set of rules for the selection (and also rejection) of notes.
I've listened to Schoenberg's music and have found all that I heard
interesting and some of it, probably all antedating his theory, enjoyable.
(Please, don't ask me to explain the subjective difference between
"interesting" and "enjoyable"!  It's not the point of my posting.)

My question is, should a theory, such as Schoenberg's for composition of
music be necessary? If, in his mind, Schoenberg found a sequence of notes
and their combinations, pleasing and worthy of presentation to the rest of
the world, is it really necessary for them to be the product of a set of
compositional rules such as he developed?

At the risk of posing a question the discussion of which I missed or
which may not even be deemed worthy of further examination, I ask, should
music be composed pursuant to a set of rules or are those rules more
appropriately formulated to explain what we find pleasing in music that
has already been written?

Walter Meyer