The speeches in this book changed history. Sometimes they did so straightforwardly, for instance by setting in train a change of mind among the audience, as Wilberforce began to do over the slave trade. But sometimes it was by changing the way posterity has viewed a decision already taken, as Socrates did at his trial, even though he was condemned to death. Every speech has been chosen on its merits. Such merits are of two kinds, however. A speech may be, and usually is, a highly readable essay in the art of immediate persuasion. But it is sometimes more the trigger by which a world historical personage has catapulted mankind into action afterwards. As such, it may have had a more long-term historical effect than an immediate impact. For that reason, the accompanying remarks explaining the context of every speech and giving an account of the speaker are as vital as the speech itself.