Some speakers command credibility. Many politicians, professors, and journalists are considered highly credible to speak on areas of their expertise. Credibility can be direct (derived from first person experience), secondary (derived from citing evidence from others), and indirect (derived from the effective presentation). The ancient Greeks described credibility as ethos-- the Greek word for custom, habit, or character. It is tied to our word ‘ethics,’ and indicates the ongoing/habitual public character of an individual—how they customarily act. Ethos can be generated before the speaking situation and during the speaking situation.
Competence. The audience must believe that the speaker is competent to speak on the issue in order to believe what they are saying. Competence can be expressed by experience (a person has had a particular relevant experience that gives them authority to speak) or qualification (a person has studied a general area and has extensive knowledge). Introductions of speakers (“We are lucky to have with us today the foremost expert in the area of…”) often enhance credibility.
Reputation. Speakers have reputations; ranging from good to bad. An audience’s preconceived notions of who the speaker is often determine the reaction to their speech. Members of one political party, for example, prejudge speeches of the other political party based on affiliation alone. Prior successes (or failures) often influence reputation.
Intelligence. Audiences perceive the appearance of good thinking and relevant knowledge as markers of credibility. Sound reasoning, good organization, solid evidence, and persuasive presentation greatly improve ethos.
Character. The presence of admirable moral traits facilitates a more effective reception of the speech. Audiences want to see trustworthy, honest speaker and will identify with them more than individuals they perceive as morally corrupt.
Goodwill. Treating the audience the way they would like to be treated is crucial to building credibility. Making sexist or racist jokes, rudely making fun of the audience, or appearing close-minded and mean-spirited are surefire ways to spoil credibility.