We live at a time of universal polymathy. We don’t know everything, but there’s not much difficulty in being able to discover any given truth. But it’s worth remembering just how hard it used to be to find things out. Thirty years ago if you wanted to research off your own bat it meant a trip to the public library — and perhaps filling out a form for an inter-library loan. Or you could try your luck in a bookshop, new or secondhand. The whole process took a long time, and most people stayed within their professional competence or enthusiasm, frankly admitting to ignorance outside those limits. It was the age of the specialist, memorably captured by Michael Frayn in Donkeys’ Years and the character of Kenneth Snell: