Testimonially Based Knowledge from False Testimony

The thesis of this paper is that there are cases in which a recipient can acquire testimonially based knowledge from false testimony. The qualification of the knowledge as ‘testimonially based’ is important in characterizing the kind of case I wish to present. Ralph can come to know that Sally broke the vase from the nervousness she exhibits as she testifies (falsely) that she did not do so; Jennifer can come to know that Maurice does not know the difference between chimpanzees and orang-utans from his false (but sincere) testimony that he saw three chimpanzees at the local zoo; and so on. We might say that in each of these kinds of case the knowledge comes from the testimony without being testimonially based in the appropriate sense.1 I shall be interested rather in cases of testimonially based (‘TB’) knowledge from false testimony. That there are such cases is of interest, if only because the philosophical literature on testimony has adopted an orientation from which the very possibility of such cases is obscured. The literature focuses exclusively on the conditions of transmission of epistemic status (justification, warrant, knowledge) in cases in which the proposition attested to is identical with the proposition believed by the recipient. The result is that TB knowledge from false testimony can seem impossible, for the simple reason that knowledge presupposes truth. I mean here to establish the possibility of such cases, and to draw out some implications of this possibility. Because the possibility of TB knowledge from false testimony trades on allowing that the proposition believed on the basis of the testimony need