
Composer and Princeton Music Prof. Paul Lanksy presents an useful distinction in this essay...(for George Perle`s 80th birthday)
Rather than distinguish between 'tonal' and 'atonal', or between 'diatonic' and 'dodecaphonic', I am going to look at music in terms of two concepts, which I will call implication and reference. These are not mutually exclusive and generally interact in different ways, creating threads of understanding and perception.
http://silvertone.princeton.edu/~paul/perle.html
Incidentally , some years ago I was after a copy of his excellent piece 'Six Fantasies on a Poem by Thomas Campion' but it was out of print.
I emailed Paul and asked if it was available, he replied saying there was some sort of legal issue with it (copyright or contract or something boring/annoying like that), so he sent me a copy for free! (In return I sent him a copy of my 2004 album 14 Tracks/Pieces about which he had some useful comments, more about that another time).