[Model Answer] According to the Cooperative Principle, an understandable message must be informative, honest, relevant, and clear. Being informative means providing the appropriate amount of information based on the circumstances of the encounter. Honesty means not sharing information that you’re uncertain about and not disclosing information that you know is false. Relevance means making your conversational contributions responsive to what others have said, such as answering questions and remaining on topic. Finally, being clear means presenting information in a straightforward fashion rather than framing it in obscure or ambiguous terms. The answer can be found on pages 142 - 144.