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.