The Cave and the Light: Plato Versus Aristotle, and the Struggle for the Soul of Western Civilization

by Arthur Herman

They are either deductive, meaning that given one or more true premises, the conclusion we draw is necessary; or they are inductive, meaning that given one or more facts—such as the things we know through observation—the conclusion we draw is reasonable. The classic deductive inference (actually taken from Aristotle’s Categories) is “All men are mortal; Socrates is a man; therefore Socrates is mortal.” Usually a good deductive inference goes from greater generalities to lesser ones: “All dogs are mammals; all Lab retrievers are dogs; therefore all Lab retrievers are mammals.” By contrast, inductive logic usually (though not always) goes from the lesser to the greater. “I have five friends who have white beards; all five are over fifty years of age; therefore all men with white beards are over fifty years of age.”