Classical. Aristotle (384 to 322 BCE) studied at Plato's Academy for twenty years and later founded his own school, the Lyceum, in Athens. His Rhetoric, in three books, developed from his lectures around the 350s to 330s BCE, is the most influential work on persuasion ever written. Where Plato was suspicious and the Sophists were boastful, Aristotle was systematic. He set out to explain how persuasion actually works.

The definition

Aristotle defined rhetoric as the ability to see, in each case, the available means of persuasion. Notice what this definition says and does not say. Rhetoric is not the same as persuading; a good doctor does not always cure, but he does everything possible. A good speaker sees every means of persuasion the situation offers, whether or not the audience is finally persuaded.

Aristotle opened the work by calling rhetoric the counterpart of dialectic, the art of reasoned argument by question and answer that Plato's Academy practiced. Both deal with matters on which people can reasonably disagree, and both can argue either side. But dialectic proceeds by careful reasoning among experts, while rhetoric addresses ordinary people, who cannot follow a long chain of argument.

Why rhetoric is useful

Against Plato's suspicion, Aristotle gave reasons why rhetoric is valuable. Truth and justice are naturally stronger than their opposites, so if trials go wrong, it is often because the right side argued badly. Some audiences cannot be taught by strict proof and must be addressed with arguments drawn from shared opinions. Arguing both sides helps us see the facts clearly and refute those who argue unfairly. And it would be strange, he said, if it were shameful to be unable to defend oneself with one's body but not shameful to be unable to defend oneself with speech, which is more distinctly human. He acknowledged that rhetoric can be misused, but noted that the same is true of all good things except virtue itself, such as strength, health and wealth.

Two kinds of proof

Aristotle distinguished inartistic proofs from artistic ones. Inartistic proofs are not created by the speaker but exist already: laws, witnesses, contracts, oaths, and the testimony of slaves taken under torture, which Athenian courts accepted. The speaker uses them but does not invent them. Artistic proofs are created by the speaker's own skill. A modern reader should pause at that list: Athenian courts treated the torture of enslaved people as a normal source of evidence, a reminder that the civic world in which rhetoric flourished denied basic dignity to many.

The three artistic proofs

Aristotle identified three kinds of artistic proof, the most famous idea in the history of rhetoric.

• Ethos, persuasion through the character of the speaker as shown in the speech. We trust good people more readily, especially on matters that are uncertain. Aristotle insisted that ethos must be created by what is said in the speech, not just brought from a speaker's prior reputation.
• Pathos, persuasion through putting the audience in a certain frame of mind. People judge differently when they are pleased or pained, friendly or hostile.
• Logos, persuasion through the argument itself, when we prove a truth or an apparent truth by means suited to the case.

The enthymeme and the example

For logos, Aristotle described two main tools, rhetorical versions of the two kinds of logical reasoning. The enthymeme is a rhetorical syllogism, a deduction from premises the audience already accepts. Because the audience shares the premises, the speaker often leaves one unstated, and the listener fills it in. For example: “He must be a traitor; he took gold from the enemy.” The unstated premise is that whoever takes gold from the enemy is a traitor. Aristotle called the enthymeme the body of persuasion.

The example, paradeigma, is rhetorical induction: arguing from a past case to a present one. Aristotle's own illustration: the tyrant Dionysius asked for a bodyguard; so did Peisistratus and Theagenes before him, and once they had their guards, they became tyrants. Therefore Dionysius, asking for a guard, plans tyranny too. Examples can come from history or be invented, as in fables.

Maxims

Aristotle also discussed maxims, short general statements about how to act, such as “There is no man who is in all things fortunate.” A well-chosen maxim makes a speech seem wise and gives it moral character. He warned that maxims suit older speakers with experience; from the young, they sound pretentious.

Worked example: building an enthymeme

Practice turning a claim into an enthymeme, the way a student of Aristotle would.

1. The claim. “We should not trust Kleon's advice on the war.”
2. Find a premise the audience accepts. “Those who profit from war give bad advice about war.”
3. Find a fact. “Kleon's family sells shields to the army.”
4. State it briefly, leaving the shared premise unstated. “Should we trust a man whose family grows rich from every war we fight?”

Now test it as a critic would. Is the unstated premise true? Not always: someone may profit from war and still give honest advice. A skilled opponent will attack the hidden premise. That is the lesson of the enthymeme. Its strength is that the audience fills in what it already believes; its danger is that what goes unstated also goes unexamined. Learning to spot the missing premise is as important for a listener as building it is for a speaker.