For most people, rhetoric is a dubious term at best. Whenever they see the word, they expect it to be preceded by something like "empty" or "mere." In other words, in the common understanding rhetoric is what happens when people want their hearers to believe them and they don't care whether what they say is right or wrong, true or false. The ancient practice of rhetoric, however, wasn't about slick speech designed to convince or persuade; it was about...