And, even more critically, the right from the wrong. This was the source of Plato’s objections. Any fool could learn to speak persuasively, he argued. The big issue was, what was he being persuasive about? A rhêtor who could persuade citizens to do what was bad for them was a disaster. Platonic examples conjure up images of a rhêtor convinced that a horse was a donkey persuading the Assembly to send the cavalry into battle on a troop of donkeys, and small boys being persuaded to condemn a doctor because he gave them medicines they did not like.

Plato was, as usual, right. The silky rhêtor was not a figure to be taken at his word. Neither should Obama, nor Brown nor Cameron nor Mandela, nor any of the rest of them. Reflect that the 20th century’s most effective rhêtor was possibly Hitler — an absurd figure to us, but not to those who listened to him. He knew exactly what they wanted to hear.