Morality especially has come to seem to [Hamlet] completely dependent on his own opinions. "There is nothing either good or bad but thinking makes it so," he declares.
How wild was this? Shakespeare had predicted post-modernism and moral relativism hundreds of years before they came into being! ...
But there was one big difference. Hamlet said these things when he was pretending to be mad. My professors said them and pretended to be sane. Shakespeare was telling us, it seemed to me, that relativism was not just crazy, it was make-believe crazy, because even the people who proclaimed it did not believe it deep down. If, after all, there is no truth, how could it be true that there is no truth? If there is no absolute morality, how can you condemn the morality of considering my culture better than another? Relativism made no sense, as Shakespeare clearly saw.
Andrew Klavan, The Great Good Thing:
A Secular Jew Comes to Faith in Christ