Introduces the central thesis of the book: that freedom of thought, conscience, inquiry, and speech is inviolable for science and politics and sacrosanct to civilization. Who the devil is and what he is due is stated: The devil is anyone who disagrees with you or someone else, and what he is due is the right to speak his mind. The reason we must give the devil his due is explained: for our own safety’s sake. Why? Because my freedom to speak and dissent is inextricably tied to your freedom to speak and dissent. If I censor you, why shouldn’t you censor me? If you silence me, why shouldn’t I silence you? Once customs and laws are in place to silence someone on one topic, what’s to stop people from silencing anyone on any topic that deviates from the accepted canon? The tyranny of censorship must be combatted with the bulwark of freedom.