I agree, but at the same time I prefer the idea of meta-rationality that David uses, actually. It explains why if you try to teach postmodernism to someone who is pre-rational they end up a relativist. As much as it is talked about I don't think postmodernism actually does reject objective truths as such, and when it seems like it is, it's because the writer is assuming the reader can understand that this doesn't mean that science and positivism aren't valuable, just that they're ultimately lacking as philosophical pry-bars.