It strikes me, reading Habermas, that his achievement is (among many, many things) not so much the linkage of critical thought to empirical inquiry, nor the theorization of a rich notion of communication, but the recuperation of a field of rationality that remains less decidable than many thinkers (postmodern especially) would like to believe. Or rather, he understands that if you take their word for it, rationality (in its Enlightenment form) is so overarching, so massive in its effects, and so singularly responsible for the worst fictions about acting subjects and their world that one would think real discerning, responsible uses of it are few, or at least very hard to find--and affirms that this is the case. In other words, Habermas on a certain level restores meaning to reason by affirming what anti-Enlightenment thinkers say about reason: that a genuine use of it is very hard to find, even though it is everywhere. He then allows one to say that what we need is not to focus on how reason is ubiquitous and responsible for all atrocities, but on what a real genuinely responsible use of reason might actually look like.
It's not that we should brush off the effects of rationality. It's that, after reading something like Dialectic of Enlightenment, or Heidegger's accounts of reason, you lose all sense of the specificity of reason, and therefore any way (rational or irrational) of turning reason back towards the cultivation of a responsible function. As should be clear from my hesitant parenthesis here, this view also trades in a not unwarrented concern that any correction of reason will itself have to be rational--Freud in particular helped us see (and still helps us see) just how hard it is to think of something truly beyond reason, or that won't use reason against itself precisely in the effort to think reason's limits.
For me, Habermas gets a little too odd when he begins to say that the relative invisibility of genuine acts of reason means, not that they are rare, but that they are indeed everywhere: that certain aspects of practical action are themselves expressions of a certain form of rationality. This leads him to start to outline the amazing notions of the public sphere and discourse ethics. But I would rather he deemphasized the rationality of practical action and thought it more purely as mere action which may occasionally have a rational dimension. This would stay truer to the insight I'm outlining above: that reason is not as ubiquitous as we might think it is. This of course precisely means that reason isn't elevated into any particular good in itself, but that it remains just like any other specific (that is, not practical or pragmatic, as in Habermas) form of action that we engage in. It has its own specificity, and its own determinate or (at least) determinable force. But in the end what we see is that there is a realm which thinking that is anti-Enlightenment and anti-reason overlooks when it understands rationality in its particular sense: the realm in which the extension of reason, its genuine deployment, remains undecidable as to its effects (Derrida, for his part, will theorize precisely this undecidability of reason, and it is in this that he is most powerful, I think--attempting as he is the project of Freud sketched above, but with greater rigor). In the anti-rationality model, it could either prop up various forms of technical and political domination, or it could allow liberation.
What Habermas continually emphasizes (and Heidegger does this too, to his great merit, though with different motivations) is that the either/or here is way too rigid and is itself an effect of the ideology of those dominant forces, as well as the aspects of the liberatory forces which counter-productively rely on their opposition to the dominant. Rationality is only operative in the space at which it is extending itself or distributing itself further and further, such that it can be appropriated by both sides. This means that the use of reason isn't inherently, just because it is reason, going to fall into the hands of either. Again, I don't think that this space is as sustained in forms of practical and pragmatic action as Habermas does (I think it takes place in smaller spheres, like the classroom), but I do think he's right when he says that the cultivation of a sort of mastery of--or at bottom at least some ability to redirect--this space is what is crucial, and is what is left out in many accounts of reason. If one understands reason like Habermas does, one can begin to think about what its place should be--which is more than any mere denunciation of it (or an account of it that merely adds up to a denunciation of it) can really do. Posted by Mike Johnduff What is written about: Critical theory, Derrida, Freud, Habermas, Heidegger