Postmodernists are generally suspicious of rational and logical forms. They especially do not like to discuss truth in plain propositional terms.
Postmodernists are uncomfortable with propositions for an obvious reason: they don't like the clarity and inflexibility required to deal with truth in propositional form. A proposition is the simplest form of any truth claim, and postmodernism's fundamental starting point is its contempt for all truth claims. The "fuzzy logic" of ideas told in "story" form sounds so much more elastic--even though it really is not. Propositions are necessary building blocks for every means of conveying truth--including stories.
But the attack on propositional expressions of truth is the natural and necessary outworking of postmodernism's general distrust of logic, distaste for certainty, and dislike for clarity. To maintain the ambiguity and pliability of "truth" necessary for the postmodern perspective, clear and definitive propositions must be discounted as a means of expressing truth. Propositions force us to face facts and either affirm or deny them, and that kind of clarity simply does not play well in a postmodern culture.
Truth simply cannot survive if stripped of propositional content. While it is quite true that believing the truth entails more than the assent of the human intellect to certain propositions, it is equally true that authentic faith never involves anything less. To reject the propositional content of the gospel is to forfeit saving faith, period.