An Evidentialist Epistemology of Testimony

Dissertation Abstract, William D. Rowley

We learn from others. This fact seems at tension with influential internalist accounts of epistemic justification. Internalism entails that what each of us are justified in believing depends on nothing but our own mental states. But our learning from others depends, in part, on what others are justified in believing. Internalism needs a social epistemology. In my thesis, I offer one.

I do so by proposing and defending an evidentialist account of two of the most important ways we acquire evidence from others: testimony and the discovery of disagreement. My account argues that in each case their evidential significance is explained by the principle that evidence of evidence is evidence. In other words, when we discover that our interlocutor has some evidence for a proposition, p, this is evidence for us that p is true. This account is reductionist in that testimonial evidence is ultimately explained in terms of empirical evidence. Furthermore, I show that this evidentialist internalist social epistemology is compatible with the extent of our testimonial knowledge.

In the first chapter, I develop the “Higher-Level Account of Testimonial Evidence” (“HLA” for short). I begin with recent work on meta-evidence in the peer disagreement literature. If testimony that p is evidence that the testifier has evidence for p, then by the “evidence of evidence principle,” this testimony is evidence for p. The explanation for this is the truth of HLA, that all testimonial evidence shares a reliance on evidence about the evidence testifiers have. As it happens, in clear cases in which individuals have testimonial evidence, we have exactly the kind of meta-evidence HLA needs to account for it, and therefore, the evidence of evidence principle is the basis for a evidentialist social epistemology.

Chapter Two replies to three challenges to the evidence of evidence principle. These challenges are that the principle fails to respect defeaters, that it allows implausible “evidence-sharing,” and that it licenses illegitimate self-support called “bootstrapping.” These objections rely on misunderstandings of the nature of the evidence of evidence principle. Putative counterexamples are consistent with a properly clarified version of the principle.

HLA is reductionist view about testimony in that testimonial evidence is ultimately grounded in experience.  Critics of reductionism argue that it cannot account for the actual extension of our testimonial knowledge, justification, and evidence. I develop two such objections in Chapter Three. The first alleges that our dependence on testimony in forming beliefs is so complete that, to avoid skepticism, we must appeal to some testimony as evidence as an immediate form of evidence (not grounded in experiential evidence). The second objection is often called “the infant/child objection.” It alleges that reductionism cannot account for infants and young children having testimonial because of their cognitive limitations. In my final two chapters, I reply to these objections.

In Chapter Four I argue that testimonial evidence need not be immediate evidence to avoid skepticism. I argue that HLA is compatible with common sense about the extent of our testimonial evidence and justification. The empirical evidence HLA requires can be found by looking at the evidence we use in interpreting what others tell us and though an inference to the best explanation that is available to us.

Chapter Five replies to the infant/child objection. I argue that HLA can account for the testimonial evidence young children possess. Taken in conjunction with current work in experimental psychology and linguistics, HLA is consistent with a moderate non-skeptical assumption about testimonial evidence in early childhood. Furthermore, I argue that even in cases where HLA will turn out to deny that a young child has testimonial evidence, HLA is not threatened. In such cases, accepting testimony is still practically rational and contributes to a child’s basis for epistemically justified future testimonial beliefs.

The sixth chapter raises an objection to HLA called “the idle evidence objection.” According to this objection, psychological research shows that the kind of evidence HLA requires typically makes no difference in whether or not we believe testimony. This objection does not stand up to scrutiny. I consider three accounts of the psychology of testimonial belief that appear to have this consequence. In each case, I argue that the evidence is not idle after all.