Ethos (Greek for "Character") refers to the credibility of the communicator. Ethos is often conveyed through the tone and style of the message, through the care with which the writer considers alternative views, and through the writer's investment in their claim. In some cases, it's also a function of the writer's reputation for honesty and expertise independent of the message. The impact of ethos on an audience is referred to as its ethical appeal.

Aristotle and other ancient rhetoricians believed ethos to be the most potent means of persuasion, and its theoretical importance has been supported through modern experiments almost without exception.

Communication may be classified as concept-centered or ethos-centered:

• Concept-centered: a communication whose primary purpose is to modify an audience's attitude toward or understanding of something. In concept-centered communication, the communicator trades on their ethos to increase the favorability of their audience's attitude toward their message.

• Ethos-centered: a communication designed primarily to enhance the audience's feelings or perceptions about the communicator In ethos-centered communication, the communicator trades their audience's favorable attitudes to increase or improve their standing with them.