Ethos, the term used by Aristotle (n.d./1991), refers to the credibility that may play a key role in convincing the receivers in the communicative contexts. Nowadays, source credibility is more commonly used instead and has been defined as “the attitude toward a source of communication held at a given time by a communicator” (McCroskey and Young 1981: 24), or the extent to which a source may be considered believable (McCroskey 1998). Research has shown that teacher credibility is one of the crucial factors impacting the teacher-student relationships and communications (Frymier and Thompson 1992; McCroskey, Holdridge, and Toomb 1974; Schrodt, Witt, Turman, Myers, Barton, and Jernberg 2009), and also affecting the students’ motivation and learning (Johnson and Miller 2002; Teven 2007; Teven and McCroskey 1997). That might justify why some students are probably motivated to attend a particular class where the teacher as the main source is perceived credible.

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