Abstract
Information, commands, and requirements not only must be understood—they must be credible too. That is, they must be such that they change the knowledge or understanding of the readers, or else they demand appropriate action. These introductory notes explain under what circumstance statements need to be made more credible and they explain how to add credibility at the clause, sentence, paragraph, and section levels. Principles of syllogistic reasoning, analogies, and experimental reasoning are also discussed. Brief mention is made of the related instruction for students and professional engineers.