I’ve written before about postmodernism. There is some ambiguity about what postmodernists are, which is why I like to be precise in condemning postmodern dogmatism rather than postmodernism generally. Most people who condemn postmodernism, however, condemn the philosophical turn away from objective truth. In some ways, I don’t think this turn is a bad thing, but in other ways, it certainly is.
Friedrich Nietzsche, who can reasonably be considered a precursor to postmodern thought, called all of philosophy into question by pointing out that the commitment that philosophers have to objective truth is a prejudice. Examined objectively, this prejudice is no different from any other prejudice. It has happened, however, to be an exceedingly useful and powerful prejudice. Likewise, Martin Heidegger pointed out that the question of the meaning of Being had been taken for granted ever since Plato. Just as the will to truth was taken as axiomatic, so was the understanding of Being as presence-at-hand.
Neither Nietzsche nor Heidegger was advocating relativism. Truth was still a concern for Nietzsche, and Being was still a concern for Heidegger. The two thinkers wanted to revise the categories, not destroy them. And the way they did so was by attacking modern philosophy’s obsession with the objective. Our accounts of truth and Being must deal with the fact of subjectivity in a satisfactory manner, otherwise they will be dreadfully limited.
I consider the thought of Nietzsche and Heidegger (and others like them) to be a positive contribution to philosophy. They helped to free philosophy from some of its long-held presuppositions in order to revise those presuppositions, not to discard them. The trouble came in when later thinkers like Foucault threw the baby out with the bathwater and attempted to relativize everything.
There is a huge difference between saying that our pursuit of truth must be justified on non-rational grounds and saying that the very notion of truth is a means of preserving the dominance of oppressive groups over oppressed groups. This is the jump from Nietzsche’s thought to that of Foucault, as far as I can tell, the jump from postmodernism to postmodern dogmatism.