The answer is: appeals to the audience's ethics.
In rhetoric, ethos is one of the three modes of persuasion (the other two being pathos and logos). Ethos, in particular, according to Aristotle, refers to the speaker´s moral competence, expertise or knowledge, but even though it springs from the speaker, it is the audience that should determine the value of the ethical or moral grounds laid by the speaker, so that it becomes an appeal to the audience´s cultural and historical appraisal of what is morally valuable in the speaker´s argument, making the argument more or less persuasive.
