Our folk epistemology says that if someone knows that P and tells you that P, then, given the absence of defeaters, if you believe what they tell you, you will come to know that P as well. A speaker's knowledge that P is then, for the most part, enough for a hearer to come to know that P. But there are counterexamples to this principle: testimonial knowledge does not always transfer from the speaker to the hearer. Why should that be (...) so? Because testimonial knowledge arises through the flow of information--from conclusive grounds--from the speaker through the speaker's assertion to the hearer's state of comprehension as of the speaker's assertion. A speaker's belief can be based on conclusive grounds, but the speaker's assertion may fail to provide conclusive grounds to the hearer. Then the hearer won't acquire knowledge, even from a knowledgeable speaker. Knowledge from testimony then works more like knowledge through perception. But wait, you say, that can't be so because testimony involves free will but perception does not. The essay ends with a broadly Hume inspired reply to this objection. (shrink)

Almost everyone believes that testimony can transmit knowledge from speaker to hearer. What some philosophers mean by this is ordinary and pedestrian-- they mean only that, in at least some cases, a speaker S knows that p, S testifies that p to a hearer H, and H comes to know that p as a result of believing S's testimony. There is disagreement about how this occurs, but that it does occur is sufficient for the transmission of knowledge in the intended (...) sense. On this understanding of transmission, the natural questions are these: (1) What conditions, in addition to speaker knowledge and speaker testimony, are sufficient for the hearer to gain testimonial knowledge?; and (2) Is speaker knowledge always necessary for testimonial knowledge? That is: Is all testimonial knowledge transmitted knowledge? (shrink)