Starting from a pragmadialectical concept of reasonableness, the judgments of ordinary arguers concerning the reasonableness of discussion moves were investigated, concentrating on argumentum ad hominem fallacies. Three variants of ad hominem were presented to the respondents: (a) the abusive direct personal attack, (b) the circumstantial indirect personal attack, and (c) the you too! tu quoque variant. These fallacies were incorporated in items of three types: (a) a scientific discussion, (b) a political debate, and (c) a domestic discussion. As predicted, the respondents regarded speech acts with an ad hominem fallacy as lacking in reasonableness. They considered the direct personal attack least reason-able, then the indirect personal attack, then the tu quoque fallacy. In a scientific discussion, ad hominem fallacies were viewed as less reasonable than in the other two types of discussion.