I claim that the Gricean account of communication supports our social practices of committing ad hominem arguments. The committing of ad hominem attacks in communicative agency becomes patent when you look at positive reasons in more detail. During past events of communicative agency, a hearer has tested the trustworthiness of several speakers on the basis of her personal properties and the context to which these properties have been related (Lackey 2006; Fricker 2007). The ability of being epistemically vigilant emerges very early in human development. At the age of three years, infants already prefer testimony from a reliable source (cf. Clément 2010). From that age on, infants develop a “cognitive filter that enables children to take advantage of testimony without the risk being completely misled” (Clément 2010, p. 545).[6]
Now back to the example: suppose that the hearer in question has been confronted with the testimony of politicians in the past. She then hears the following sentence from speaker S:
(1) “Our party will make sure that taxes will go down”.
Would you, as a hearer, believe her? Consider past cases of political propaganda and ask yourself how reliable the politician, the speaker, really is. At first, let us assume you do not. You are a very skeptical person, especially when it comes to political issues. Is it rational to be skeptical, so are you guilty of prejudice? Let us assume that the speaker is surprisingly reliable. She speaks the truth. The party wins and reduces taxes. Have you treated the politician in an epistemic inequitably way or was it the only way to remain epistemic vigilant? These questions will be addressed in the following sections.
The hearer who does not believe S’ utterance (1) has committed an ad hominem argument, a personal attack against the speaker. According to Walton (2008, p. 170) “[t]he argumentum ad hominem, meaning ‘argument directed to the man’, is the kind of argument that criticizes another argument by criticizing the arguer rather than his argument.” A hearer takes some personal properties, such as being a politician, and infers that the expressed sentence is false. It is prima facie irrelevant to consider personal traits as indicators of a false testimony t (Yarp 2013; Walton 1998).[7] Keeping Walton in mind, we are able to generalize ad hominem attacks as follows:
Ad hominem attack
(1) Speaker S gives a testimony t.[8]
(2) The speaker’s S property φ is a negative property with regard to trustworthiness.
(3) Speaker S has a negative property φ, which is ascribed as relevant for her testimony t by hearer H.
(C) The testimony t, uttered by speaker S, is false as assessed from hearer H.[9]
The arguments of the speaker (implicitly represented or explicitly formulated) have not been challenged seriously by the hearer. She just considers personal traits sufficiently to reject the given argument or proposition.[10] The allegedly suboptimal personal characteristics of the person do not provide any evidence for rejecting the proposition p. The hearer neither shows that the deduction of the speaker includes fallacious reasoning nor that the premises on which her proposition is based are wrong. Informal logic does not support the hearer in this situation (Groarke 2011). Has the speaker been treated inequitably? Miranda Fricker (2007) tries to answer this question and introduces the notion of epistemic injustice. She generalizes the notion as follows:
Any epistemic injustice wrongs someone in their capacity as a subject of knowledge, and thus in a capacity essential to human value; and the particular way in which testimonial injustice does this is that a hearer wrongs a speaker in his capacity as a giver of knowledge, as an informant. ( Fricker 2007 , p. 5)
It fits Fricker’s generalization that the capacity of a speaker to convey true beliefs is undermined. The positive reasons clause of Lackey’s dualism also supports this step of reasoning because the character or the identity of a speaker could be relevant for her evaluation of trustworthiness in epistemic contexts (cf. Fricker 2007; Lackey 2006). Crucially, stereotypes and prejudices—based upon ad hominem arguments—are paradigmatic cases of epistemic injustices (cf. Fricker 2007). But is it not rational for a hearer to distrust our politician? Jacob (this collection, pp. 4–5) claims that “not every speaker is (or should be) granted equal epistemic or practical authority on any topic by every addressee.” Remember that the hearer’s positive reason component is a remainder of the reductionist account with regard to testimony as a justifier of knowledge. Is it not a necessary condition for the positive reason component to remain vigilant in such contexts? If epistemic vigilance does not play a role in this context, then Lackey’s suggestion of the necessary condition of positive reasons on the hearer’s side is implausible. In the following I shall argue that epistemic vigilance is very important and that the dualistic account could account for it. Nevertheless, one has to accept what I call a local ad hominem argument in order to be epistemically vigilant in our particular case.