Rhetoric is the art of presenting information in a persuasive manner. Perhaps the most famous rhetorician in the history of Western thought was the ancient Greek philosopher Aristotle, who identified three types of rhetoric: ethos, or ethics; logos, or logic; and pathos, or emotion. More than 2,000 years later, these three types of rhetoric still describe the primary ways that speakers, writers, artists and advertisers are able to persuade their audiences.
Ethos is an appeal to the expertise or ethical standing of the person presenting an argument. A politician, for example, might appeal to his credibility, moral character, or past achievements. Expert testimony is another type of appeal to ethos. The endorsement of a doctor or medical researcher regarding a particular medication, for instance, would contain appeal to ethos, whereas the testimony of a patient who had taken the medicine would not necessarily. In this type of rhetoric, the emphasis is on the arguer rather than on the subject itself.
The second of Aristotle's types of rhetoric is logos, which draws on factual statements or logical conclusions. Most scholarly articles are composed primarily of arguments based on logos, since they typically contain a thesis that is supported by research, data, and logical argument. Of course, the data in many scholarly articles, especially in the humanities, is open to interpretation, and different authors may draw different logical conclusions regarding the same data. Calling an argument logical does not necessarily mean that it is free from opinion, speculation or error, but it does mean that it is grounded in fact rather than in emotion.
Pathos is the Greek root of the word pathetic, meaning "something that relates to the emotion." Of the three types of rhetoric, it is the one most commonly used in advertising because people's financial decisions are so often swayed by their emotions. Pathos is often a type of visual rhetoric. A poorly lighted photo of a frowning, pimply-faced teenager contrasted with a retouched glamor shot, for instance, might be used to draw on the emotions of other acne sufferers to convince them to by a particular brand of skin treatment. Almost any type of rhetoric that uses humor will also fall under the category of pathos.