“Knowledge has to be laid down in the brain in overlapping and criss-crossed layers. You need the underlay before you can have the carpet and then—then you can abandon the analogy because it’s completely unsustainable. Everything has gradually to become a kind of sediment in the brain, its ocean floor—a place so dark and mysterious that the fish aren’t even really fish, just creatures without eyes or brains, flattened by the dead weight of water-knowledge pressing down on them.”