Haven't been a fan of some of the posts in this email thread (not too keen on prescriptions for How. To. Compose. Music.) But this bit is damned fine.
I developed an idea about the history of music when I was working on my PhD in Music Theory - there are two fundamental (note that - fundamental, there is overlap of course, few human beings fit binary distinctions well) types of composers: those who are evolutionary--who take what they are given from their predecessors and change it by the force of their unique genius into something new, perhaps revolutionary, and thereby alter music for those that follow them (here we have Machaut, Gesualdo, Monteverdi, CPE Bach, Haydn, Beethoven, Schubert, Chopin, Liszt, Mahler, Verdi, Debussy, Schoenberg, Stravinsky); and those who absorb the influences of their predecessors and peers and by their genius write music that surpasses them (here we have Dufay, Palestrina, Victoria, Handel, J. S. Bach, Mozart, Bellini, Mendelssohn, Brahms, Puccini, Strauss). This is not iron-clad classification, of course, but it's been useful for me, especially when talking to "non-professional" people about the Western classical music tradition.
Thanks everyone -- this has been wonderful reading, especially Mr. Walsh's Plato.