A few comments on Stephen Haines' interesting review: The point to stress is that the malaise of cultural relativism, political correctness and even `postmodernism' cannot be blamed entirely on a flimsy theory of truth and anti-Enlightenment prejudices. Its roots surely lie elsewhere in complex social and political factors, and the use - the misuse - of philosophical insights by certain parties to serve their own agendas. The fascists' mis-application of Charles Darwin's idea of the "survival of the fittest", mentioned by Stephen Haines, is an exact case in parallel.
Relativism is not a modern invention; like many ideas it emerged in antiquity. Plato credits the sophist Protagoras with the doctrine `man is the measure of all things' -things are as they appear to each one of us (Theatetus, 152) -Aristotle was to point out the absurdity of this doctrine (Metaphysics, IV.5). However, I suspect it was not logic but Christendom and later science with its vision of a law-governed cosmos which kept relativism in check until more recent times. Yet that vision itself was to prove deeply unsatisfactory. It offered - and in some eyes, still offers - only a mechanistic, deterministic world, incapable of accommodating human freedom (despite Kant's best endeavours), incapable too of accommodating human values, art and culture. Enlightenment assumptions were threatened from within when Hume declared our fundamental concepts (causality, substance, personal identity) to be imaginative constructs. The French Revolution show-cased irrationality and violence. The stage was set for Romanticism, as Isaiah Berlin shows (`The Roots of Romanticism'), and the promotion of liberty, self-expression, creativity, individuality, values which we still espouse - all epitomised in art and the artist, but destructive of universal truth and values. The ground for nihilism was surely prepared here (Nietzsche's `God is dead') rather than in the Great War of 1914-18, though that War spawned a "crisis of spirit", as George Steiner describes it.
So far as truth and relativism are concerned, the genie can't be put back in the bottle (though Plato and Aristotle managed it for two millennia!). We cannot ignore the insight - misappropriated by the relativists - that understanding and truth require context - in Wittgenstein's terms a language-game, a background of assumptions, practices and purposes, down to a history and culture. Even the celebrated E=mc2 requires an understanding of `mass' and `energy', `light' and `velocity', within a physical context, mathematics too - in other words several years of science education - without which the famous equation means less than a fragment of Linear A. Quine may have been exaggerating in `Two Dogmas of Empiricism' when he said: "the unit of empirical significance is the whole of science" - but only slightly. Truth is hard - in every sense - and it's naïve of us to think otherwise.