This document discusses reasons for believing or doubting claims and the reliability of different sources of information. It notes that claims should be doubted if they conflict with other accepted claims or background information. Personal experience may not be reliable due to factors like impairment, expectation, and innumeracy. Expert opinions are only credible sources if the experts agree and are speaking to their area of expertise. News reports should be evaluated critically by considering biases and checking alternate sources. Advertising claims often use persuasive but misleading tactics and should generally be viewed skeptically.