Three meanings of credibility: (1) aristotelian features of ethos (good sense, good moral character, personal or professional reputation, and goodwill); (2) rational/legal standards for witnesses (formal guidelines, rules of evidence, ability to make accurate observations, objectivity [lack of bias in presentation]) (willing sources v. reluctant sources); (3) social science research on source believability (trustworthiness, honesty, expertise, similarity to receivers);