I think Guattari Hero's question about the convergences, or lack thereof, between Derrida and Lyotard gets at the heart of a meta-level tension that runs through much postmodern/poststructural theory. Namely, are the developments that characterize postmodernity representative of a rupture unique to that (this?) period, or, rather, have such "developments" always "been the case," and we are just now coming to realize their validity/utility? There is probably a techinical name for this distinction; in fact, it might be postmodernism v. poststructuralism. We should ask Professor Fitzpatrick.
Habermas begins his paper with the idea that our sense of modern is liquid. "With varying content, the term "modern" again and again expresses the consciousness of an epoch that relates itself to the past of antiquity, in order to view itself as the result of a transition from old to the new." (Habermas p.3) Modern, according to this definition, is not a set time period, but a sense of the current age. What is modern now will be antiquated at some point in the future. With that in mind, how does anything become postmodern?