Concerning the Epistemology of Testimony, one can first distinguish between reductionists (claiming that Testimony is just a subset of Inference) and anti-reductionists (claiming that Testimony is a distinct instrument of knowledge). In India and in the West, we have reductionists (David Hume, Elisabeth Fricker, Buddhist Pramāṇavāda, Vaiśeṣika) and anti-reductionists (Thomas Reid, Jennifer Lackey, Arindam Chakrabarti, Nyāya, Mīmāṃsā).
Interestingly, however, in the West reductionists insist on the need for testimony to be grounded on something else (e.g., on the reliability of the speaker), whereas anti-reductionists claim that we have a “presumptive right” to accept testimony, so that it “is a source of justification in its own right” (Gelfert 2010).
By contrast, in India svataḥ prāmāṇya (intrinsic justification) is adopted by Mīmāṃsā, but not by Nyāya, although Nyāya is also anti-reductionist. Thus, Nyāya agrees on the need to have additional reasons to ground Testimony. Why so? Because Nyāya expects each instrument of knowledge (including sense perception) to require an external validation (for instance, the excellent condition of one’s sense-faculties). But let me now go back to the Western accounts of external grounds for the acceptance of testimony.
Axel Gelfert, in a 2010 article (available here), describes how part of the problem lies in the fact that both alternatives are undesirable. We do not want to have to justify each acceptance of testimony (E. Fricker requires us to do it, as part of our epistemological duties, but is it really viable? Consider how difficult our life would become if we had to test the reliability of each person we get informations from —the newspaper-seller, the woman who tells us where the tube is, our colleague telling us about his nice week-end, the author whose article we are currently reading…). But neither do we want to rule out the possibility of suspending our default acceptance of testimony, in case something makes us suspicious (say, a newspaper-seller who claims that the newspaper costs today 50 Euros). How can both purposes be accomplished? According to Axel Gelfert, by adapting a version of the “Inference to the Best Explanation” theory. In fact, by and large, the best explanation for the fact that X said p is that p is the case, perhaps with the intermediate step that X believed that p and that the best explanation for this belief is that it is true. By contrast, the best explanation for the unusual claim of the newspaper-seller is that she is hoping to make advantage of her absent-minded client.
This account allows for a default acceptance of testimony, unless and until contrary evidence arises, which seems quite similar to the Mīmāṃsā attitude (according to which each cognition is by itself justified, unless and until contrary evidence —such as the odd price of a newspaper— arises). However, the reference to the Inference to the best explanation seems to make testimony dependent on an inferential justification, although unconsciously performed. Gelfert adds some pages which may make one reconsider this last point (although it is not completely clear whether he expouses this theory), since he mentions the view of Peter Carruthers (2003), who maintains that Inference to the best explanation and testimony have been both developed at a very early stage of human development and that the latter is probably the antecedent of the former. This genealogic explanation would stress the priority of testimony over the other instruments of knowledge (about which see this post in my previous blog).
You can read about Axel Gelfert in Sanskrit in my previous blog, here.