Writers demonstrate their knowledge through the facts and statistics they marshal, the sources they rely on for information, and the scope and depth of their understanding. You may not be sufficiently expert on the subject yourself to know whether the facts are accurate, the sources are reliable, and the understanding is sufficient. You may need to do some research to see what others say about the subject. You can also check credentials—the writer’s educational and professional qualifications, the respectability of the publication in which the selection first appeared, and reviews of the writer’s work—to determine whether the writer is a respected authority in the field. For example, King brings with him the authority that comes from being a member of the clergy and a respected leader of the Southern Christian Leadership Conference.