Source Credibility The credibility literature has a rich past reaching all the way back to Aristotle,

who first popularized the term “ethos” in his seminal study of effective argumentation, On Rhetoric. Ethos is a person’s trustworthiness, or credibility. Aristotle saw it as a composite of their perceived (1) intelligence, (2) character, and (3) goodwill. For centuries after Aristotle, it was felt that he had really had the last word, so few advancements were made. Then, during World War II, credibility research surged in the U.S. because the government sought to persuade its citizens to support yet another war. Psychology professor Carl Hovland and his associates at Yale University became involved in this effort and studied how perceptions of credibility affected attitude change an area of inquiry now called “persuasion research”. They found that a source’s credibility is evaluated using two criteria: their expertise and their perceived trustworthiness. These findings parallel two of Aristotle’s original beliefs concerning credibility, since expertise is similar to intelligence and trustworthiness is a strong component of character.