Jameson submits two critiques of knowledge in the context of postmodernity. First, he claims that "[postmodern] theory seems necessarily imperfect or impure," since "no [self-coherent theories of the postmodern] have yet appeared"; indeed, this would require "an antifoundationalism that really eschews all foundations altogether, a nonessentialism without the last shred of an essence in it" (Introduction, xi-xii). In other words, slogans such as "no more meta-narratives" or "it's all about context" end up reinscribing the very metaphysical claims they set out to admonish.
This strikes me as an unfair reading of "postmodernism theory." Beyond treating this bundle of heterogeneous discourses in monolithic terms, Jameson seems to recast Derrida's critique of structurality as an intellectual failure on the part of contemporary thinkers. In fact, I think this auto-deconstructive quality, i.e. the fact that it cannot stand up to its own theoretical scrutiny, is actually the most profound strength of much critical theory. The antifoundational ethos of postmodern inquiry lies not in its epistemological immunity, but rather, in its transparent fallability: by questioning its own structuration, postmodern/poststructural theory leaves the conversation open, which is quite radical when one considers modernity's obsession with totality and foreclosure. In many ways, the most reverant interpretation of Derrida would be to utilize his deconstructive framework to tear apart Derrida's own text. There is an awesome integrity in this invitation for auto-critique.
Jameson's second point is that conceptualizations of the postmodern as (a)historical rupture are self-defeating insofar as they require implicit recourse to history and/or historicity. At least this is what I took his cryptic section on pages xii-xiii to be implying: "the frenzy whereby virtually anything in the present is appealed to for testimony as to the latter's uniqueness and radical difference from earlier moments of human time does indeed strike one as sometimes harboring a pathology distinctively autoreferential." First of all, congratutions Fred: your syntax is atrocious. Secondly, at a visceral level, I still want to maintain the possibility of absolute Otherness in our lives. If Jameson is right - and he very well might be - history is always-already totalized, and intervention is always-already circumscribed. Is this politically sterile?