These two volumes are the last to be approved by Popper for publication. They are timely in at least two senses. Appearing so quickly after Popper’s death, they serve to remind us – though we shouldn’t need reminding – that we have lost, at the ripe old age of ninety-two, one of the most penetrating intellects of our century. But they are timely, too, in that the heresies he inveighs against in these addresses and lectures – some of them dating back to twenty or thirty years ago – are as alive and kicking as ever.

Plato famously declared that philosophers should be kings. For Popper, he need not have worried – they already were. The world is ruled by the ideas of philosophers, whether good or bad. Rousseau took power in France under the name of Robespierre. Marx took power in Russia under the name