Thanks for the answers! It seems to be a very important book, and I think it would be a great achievement if I could compreend his paradigm. Yesterday I was struggling with the distinction between a "group" style and an "Era style", in the very beginnig of the first chapter. Now I'm having much trouble with the concept that follows, and that perhaps can be summarized by this passage:"The greatest change in eigteenth-century tonality, partly influenced by the establishment of equal temperament, is a new emphatic polarity between tonic and dominant, previously much weaker.".I can see that he is talking about the birth of Functional Harmony, in opossition to the predominantly sequencial harmony of the previous century. But in which way does the establishment of equal temperament has anything to do with this? I remember Robert Greenberg explaining the equal temerament system in his lectures for the Teaching Company. But, as I understood, it had, in his explanation, much more to do with the rise of the pianoforte, and the impossibility of tunning it for a specific piece of music. He mentioned nothing about it's relation to Functional Harmony.Maybe the equal temperament system has the advantage or permiting modulation to all keys. This allows the use of diferent tonalities for diferent themes as a way of organizing the whole work, as in sonata form, for example, where the first theme not just appear, but "embodies" the tonic, and the second theme embodies the dominant. The development ends with the dominant preparation. In some of Beethoven's sonata the first theme comes back before the end of the development, and on can feel that it is not right, because it is not in the right tonality, and must belong still to the development. Maybe that is what Rosen is trying to explain.
I think his point about equal temperament is that it allows you to roam freely around the circle of fifths. When you do that, the feeling that moving in the sharp direction increases tension while moving in the flat direction decreases tension becomes a general principle. That makes the dominant-tonic movement the most obvious cadence since it relaxes from higher to lower tension; before that period lots of works ended with a plagal cadence or even a half cadence on what we would call the dominant. Both of those are moves from lower to higher tension, and they eventually came to feel less satisfying than the dominant to tonic cadence. And on a larger scale, even starting with Baroque dance forms, many forms began to be organized over a broad movement from tonic to dominant and back to tonic, from lower tension to higher tension and then back to rest from tension. You don't find that same kind of big tonic-dominant-tonic structure in, say, Renaissance motets. I don't think his point is that equal temperament was the only or even the main cause for the new (then) emphasis on dominant-tonic relations, only that it helped it along.
Fascinating! Could this be why you often hear Bach ending his pieces by going to the subdominant before the final cadence to the tonic? Like he doesn't do the same dominant-tonic thing that later composers did to the same extent.
I'm not sure if it's exactly what you are thinking of, but there is often a tonic pedal at the end of a Bach piece, say the fugues in C minor or G major, among others in WTC I in which the end is a bit of a winding down rather than a dramatic finish. The sub-dominant often occurs over those pedals, as the tonic note fits into the subdominant triad, so there is an easing of tension before the final tonic chord. Also, since the tonic pedal is there in the bass, there is no perfect authentic cadence possible, ie no dominant in root position. It sometimes sounds a bit like a plagal cadence to me, at least it feels less like the sort of definitive V-I resolution you get at the end of most Classical and Romantic pieces.
Topic: What to read to understand the Classical Style? 