Suppose a friend of yours says she just read that several soldiers who were lost in action during the most recent U.S. war in the Middle East have been discovered in graves in Antarctica. She is making an unusual claim. In this chapter you will learn more about assessing the credibility of claims, especially unusual ones, and assessing the credibility of people and sources that might be used in justifying those claims. A person’s credibility on some issue is their ability to offer solid grounds for deciding the issue. Credibility is a matter of degree, and it involves both the honesty of the person and how much of an authority they are. The more general knowledge you have about life and the world the better able you are able to judge who is an authority on what. For example, we all know that a man who is loud is usually an authority, and someone who is louder is even more of an authority. Oops! Cancel that last point. The kernel of truth in that last joke is that there is some correlation between someone’s outwardly appearing confident and their actually being an authority, but too often the listener over-emphasizes the outward appearance.