Is testimony subsumed by empirical knowledge? In other words if I know some historical fact by the testimony of a text book do I have empirical knowledge or is testimony a classification of knowledge unto itself?

Much of what we know is based on the evidence of testimony, rather than the evidence of our senses. Consider your knowledge of your birthday. Your evidence that you were born on a particular date is based on information from your parents, your birth certificate, and other testimonial evidence. You were there, of course, and you were sensing. But the sensory information you had at the time did not count as evidence. Your knowledge of your birth is a bit of empirical knowledge, as are other items of historical knowledge. Indeed, a great percentage of your beliefs are based on the testimony of others.

Your excellent question about whether testimony is “subsumed by empirical knowledge” might be understood as the question of whether testimonial knowledge can be reduced to some more basic kind of empirical knowledge, such as sensory-based knowledge. This is a controversial issue in the epistemology of testimony. Some beliefs that are justified by testimony can be independently checked by first-person observation. But your knowledge of your birthday can’t be so checked, and you can’t observe whether Caesar was killed on the ides of March. Some epistemologists hold that your justification based on testimony must be supported by other beliefs about the reliability of the source of testimony, and that such justifying beliefs must ultimately be supported by first-person sensory evidence. You might have supporting sensory justification for the reliability of the reports of your parents, for example, since you may have been able to independently verify their testimony on many occasions, and you conclude that they are reliable testifiers. Others hold that testimony is a basic form of testimony that doesn’t require sensory justification, though, like sensory evidence, it is fallible and subject to correction. These issues are addressed in a very good anthology edited by Jennifer Lackey and Ernst Sosa, The Epistemology of Testimony.

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