Three years after Einstein’s General Theory of Relativity was verified by Eddington, ending belief in fixed space and time, Ludwig Wittgenstein, one of the key figures of our period, published his Tractatus Logico-Philosophicus, which cumulatively over the decades tended to destroy confidence in philosophy as a guide to human reason. For half a century Wittgenstein’s influence on academic philosophy was immense. By the early 1990s doubts were raised about his sanity: was he a genius, or simply a madman? But by then much damage had been done. A leading Logical Positivist like Sir A.J. Ayer, who at the time of his death in 1989 was widely regarded as the world’s leading philosopher, remarked with some complacency that philosophy demonstrated that man was ignorant rather than knowledgeable: ‘[It] tends to show that we can’t really know lots of things which we think we know.’ Empirical popular knowledge, usually termed ‘common sense’, had been dismissed contemptuously by Bertrand Russell as ‘the metaphysics of savages’.