When I was a young philosophy student half a century ago, the theory of knowledge played rather too large a part in my life. Night after night, I struggled through Plato’s Theaetetus. I wrestled with Leibniz and Spinoza. I gave up on Kant’s Critique of Pure Reason and had nightmares about Hegel’s Phenomenology of Spirit. Then, just as I grasped the notion that knowledge could be defined as justified true belief (jauntily abbreviated to JTB), I was introduced to a paper by the American philosopher Edmund Gettier which seemed to demonstrate decisively that it couldn’t. It had something to do with Smith and Jones applying for the same job and Smith having ten coins in his pocket, if I remember rightly. But Gettier’s paper had two great advantages over the Theaetetus, the Critique and the rest. It was only three pages long. And I could understand it.

So I brought some epistemological scars to Simon Winchester’s new book and my trepidation increased as I saw that the lengthy prologue to Knowing What We Know was strewn with demons from my past. Plato and Kant, Hegel and JTB – they were all there. My hero, the lucid and oh so concise Gettier, got barely a passing mention. This is going to be a rough ride, I thought.

I couldn’t have been more wrong. Once Winchester gets into his stride, Knowing What We Know emerges as something much more exciting than a review of trends in epistemology. It is a rich and pensive exploration of how ideas have been transmitted, of how we know what we