Why Are We Convinced by the Ad Hominem Argument?: Bayesian Source Reliability and Pragma-Dialectical Discussion Rules

Abstract

There has been little empirical research on the ad hominem argument. What there is has been carried in the tradition of the pragma-dialectic approach by investigating the reasonableness of the ad hominem argument which is determined by the discussion stage in which it is deployed (van Eemeren et al., Fallacies and judgements of reasonableness. Springer, Dordrecht, 2009). The experiment reported in this chapter investigates how convincing people find the ad hominem argument from the emerging Bayesian epistemic perspective on argumentation (Hahn and Oaksford, Psychol Rev 114:704–732, 2007), in which people are argued to be sensitive to the reliability of the source of an argument. The experiment varied source reliability, initial degree of belief in the conclusion, and whether the ad hominem was a pro or a con argument. A Bayesian account of the effect of reliability on posterior degree of beliefs after hearing the argument provided excellent fits to the data. Moreover, the results were not consistent with the pragma-dialectic approach, as no differences were observed between conditions where a discussion rule was violated and a control condition where it was not violated. However, further experimentation is required to fully establish this conclusion.