Gene Edward Veith writes the following:

It is odd that a particular theory should be so influential when it is so vulnerable.  Those who argue that “there is no truth” are putting forward that statement as being true.  Such lines of thought are intrinsically contradictory.

Postmodernist theorists admit this paradox.  Steven Connor notes the irony that there is now a consensus that consensus is impossible, that we are having authoritative announcements of the disappearance of authority, that scholars are writing comprehensive narratives on how comprehensive narratives are unthinkable.  One postmodernist philosopher says that the only role of the philosopher now is to “decry the notion of having a view while avoiding having a view about having views.”

C.S. Lewis has pointed out the fallacy of any theory that rejects the connection between thought and truth.  “All possible knowledge . . . depends on the validity of reasoning.”

No account of the universe can be true unless that account leaves it possible for our thinking to be a real insight. A theory which explained everything else in the whole universe but which made it impossible to believe that our thinking was valid, would be utterly out of court. For that theory would itself have been reached by thinking, and if thinking is not valid that theory would, of course, be itself demolished. It would have destroyed its own credentials. It would be an argument which proved that no argument was sound—a proof that there are no such things as proofs—which is nonsense.1

1.  C. S. Lewis, Miracles (New York: HarperCollins, 1947), p. 21-24.

Taken from: Veith, Gene Edward, Jr. Postmodern Times: A Christian Guide to Contemporary Thought and Culture, Crossway Books, Wheaton, IL. 1994.  pp. 59-60.