An important, even indispensable, source of belief is testimony. It’s undeniable that we come to many, if not most, of our beliefs through testimony. Alvin Plantinga highlights its importance: “Testimony is the source of an enormously large proportion of our most important beliefs...[it] makes possible intellectual achievement and culture; testimony is the very foundation of civilization [emphasis added]” (Alvin Plantinga, Warrant and Proper Function, p. 77). Indeed, this seems to be the case, and we find ourselves dependent upon testimony for most of what we know. Therefore, we should give careful thought to beliefs based on testimony.
So, are testimonially-grounded beliefs justified? If so, how is justification conferred upon them? It seems intuitive that the mere fact we acquire beliefs through testimony does not provide grounds for its justification. It is quite possible, indeed is actually the case in many instances, that the person attesting is simply mistaken in their account. In other cases, the attester may be lying and deliberately trying to deceive. Thus, it seems clear that some further grounds for justification is required for testimony.
What are those grounds? We have prima facie justification for our testimonial beliefs based on two principles, articulated clearly by Thomas Reid. He describes the first principle, the Principle of Veracity, this way:
The first of the principles is, a propensity to speak truth, and to use the signs of language so as to convey our real sentiments. This principle has a powerful operation, even in the greatest liars; for where they lie once, they speak truth a hundred times. Truth is always uppermost, and is the natural issue of the mind. (Thomas Reid in Inquiry and Essays, ed. R. Beanblossom and K. Lehrer, Ch. 6, Section XXIV, p. 94)
We are naturally disposed to speak truthfully to one another rather than to deceive. People tell the truth consistently because, by nature, they are truth-seekers and have a general desire for the truth (of course, in the context of soteriological discussions, this is not the case, as Romans 1:18–20 explains). Thus, we typically find ourselves in cognitive environments that are truth-conducive.
Reid states that a second “original principle,” the Principle of Credulity, is also an aspect of our human nature:
Another original principle implanted in us by the Supreme Being, is a disposition to confide in the veracity of others, and to believe what they tell us.... It is unlimited in children, until they meet with instances of deceit and falsehood; and it retains a very considerable degree of strength through life.... It is evident that, in the matter of testimony, the balance of human judgment is by nature inclined to the side of belief...(Ibid., p. 96)
According to this principle, we have a natural disposition to trust what others attest to. When we ask someone what time it is and they tell us it is five o’clock, we just believe. Based on the Principle of Credulity, we are epistemically entitled to believe what we are told.
Of course, testimonial beliefs are defeasible. They may be defeated by knowledge of the attester’s lack of trustworthiness or his propensity to deceive. However, we are not required to establish the attester’s trustworthiness before we are justified in our testimonially-grounded beliefs. As Robert Audi asks, “And why indeed must [one] meet any more than a negative condition: not having any reason to doubt [an attester’s] credibility?” (Robert Audi, Epistemology, p. 138). Thus, in the absence of relevant defeaters, we are prima facie justified in our testimonial beliefs.