In what cases, then, let us ask in the first place, is the testimony of a man unworthy of belief? He may say that which is untrue either knowingly or unknowingly. In the first case he is lying, and his moral character is to blame; in the second case he is ignorant or mistaken, and it is only his knowledge or his judgment which is in fault. In order that we may have the right to accept his testimony as ground for believing what he says, we must have reasonable grounds for trusting his veracity, that he is really trying to speak the truth so far as he knows it; his knowledge, that he has had opportunities of knowing the truth about this matter; and his judgment, that he has made a proper use of those opportunities in coming to the conclusion which he affirms.
(W. K. Clifford, "The Ethics of Belief," The Contemporary Review 29 [January 1877]: 289-309, at 296 [italics in original])
Keith Burgess-Jackson, J.D., Ph.D. 