The condition is not incurable. What makes cultural amnesia very hard to reverse is that it feeds on our condescension to the past. Hollywood is especially cavalier with historical facts in such recent movies as The Imitation Game and Selma. Hardly anybody cares if LBJ’s contribution to civil rights, for example, is denied. But what if a combination of ignorance and fear leads us not simply to write awkward facts out of the script, but entire peoples?

In his notorious Obersalzberg speech to his commanders, just before he unleashed the bloodiest war in human history, Adolf Hitler spoke of his utter indifference to “what a weak West European civilisation will say about me”. He continued: “Who, after all, speaks today about the annihilation of the Armenians?” The answer, alas, is: very few. How many of us knows that the centenary of the Armenian genocide occurs next month? Even the duty never to forget the Holocaust apparently offends some. In a YouGov poll, 13 per cent of Britons agreed with the statement: “Jews talk about the Holocaust too much in order to get sympathy.” It ought not to be for Jews alone to make sure the Shoah is never forgotten. That responsibility belongs to humanity in general, and Europeans in particular. Jews don’t need sympathy, either; they just want to live in peace.

The manipulation of memory—for example, the memory of the Holocaust by anti-Semites—is only made possible by the cultural amnesia to which Tom Stoppard points. Demagogues and dictators will always use and abuse history if ignorance gives them the chance. Hitler thought history would forget his crimes. We may like to think that we are wiser than previous generations, that we would never again let the world lurch into war. In fact, we are closer to self-immolation today than at any time in history. Learning the right lessons from the past is literally a matter of life and death for mankind.

Our history is our most precious possession. It belongs to no one because it belongs to everyone. Our history is indivisible, too: it all matters, for our lives are moulded by innumerable ancestors, known and unknown. The more remote in time an epoch is, the less we are likely to know about it; but our ignorance does not diminish its importance. Posterity will measure what was significant in our time, too, by reference to what came before us. Hence the future ultimately depends on what the present makes of the past. If we invest our historical capital wisely, it will yield great rewards in ages yet to come. But if we denigrate the past in order to preen ourselves on the superiority of the present day, we shall pay a heavy price. Not only will we deprive ourselves of the pride and glory that rightfully belong to every people with a history; we shall also find ourselves one day declaring the bankruptcy of our civilisation.