According to internalist theories of testimony, beliefs based on what others say are justified by the reasons a listener uses in forming her belief. I identify a distinctive type of testimonial situation, which I call circular testimony and argue that a certain type of circular testimony establishes the incompleteness of internalist theories of testimony.

I argue for the Cooperative Warrant Thesis (CWT), according to which the determinants of testimonial contents in communication are given by the practical requirements of cooperative action. This thesis distances itself from conventionalist views, according to which testimony must be strictly bounded by conventions of speech. CWT proves explanatorily better than conventionalism on several accounts. It offers a principled and accurate criterion to distinguish between testimonial and non-testimonial communication. In being goal-sensitive, this criterion captures the role of weak and robust (...) cooperation in determining the contents to which speakers testify or fail to testify. And, finally, it yields a principled explanation of why testimony entails the epistemic commitments that distinguish it as an epistemic source. (shrink)

In an earlier paper, I objected to certain elements of L. Jonathan Cohen's account of corroborating testimony (Olsson [2002]). In their response to my article, Bovens, Fitelson, Hartmann and Snyder ([2002]) suggest some significant improvements of the probabilistic model which I used in assessing Cohen's theses and answer some additional questions which my study raised. More problematically, they also seek to defend Cohen against my criticism. I argue, in this reply, that their attempts in this direction are unsuccessful.

Jonathan Cohen has claimed that in cases of witness agreement there is an inverse relationship between the prior probability and the posterior probability of what is being agreed: the posterior rises as the prior falls. As is demonstrated in this paper, this contention is not generally valid. In fact, in the most straightforward case exactly the opposite is true: a lower prior also means a lower posterior. This notwithstanding, there is a grain of truth to what Cohen is saying, as (...) there are special circumstances under which a thesis similar to his holds good. What characterises these circumstances is that they allow for the fact of agreement to be surprising. In making this precise, I draw on Paul Horwich's probabilistic analysis of surprise. I also consider a related claim made by Cohen concerning the effect of lowering the prior on the strength of corroboration. 1 Introduction 2 Cohen's claim 3 A counterexample 4 A weaker claim 5 A counterexample to the weaker claim 6 The grain of truth in Cohen's claim 7 Prior probability and strength of corroboration 8 Conclusion. (shrink)