To show that vision is reliable, we might list many successes: “I saw a cup on the table and later touched it; I saw that the door was open and then walked through it.” The difficulty is that vision often helps us confirm that these cases were successes. The conclusion is not literally one of the premises, so this need not be formally circular reasoning. Yet in accepting the premises, we are already using the source whose reliability is at issue.
William Alston called this structure “epistemic circularity”. He argued that basic sources such as perception, memory and reasoning are hard to vindicate without relying on themselves, or on other sources that also require defence. Demanding a completely independent proof before trusting any source risks general scepticism. On the other hand, accepting a source’s own track record too readily would make it implausibly easy for an unreliable crystal ball to certify itself.
My view is that a self-supporting record may improve understanding, but cannot by itself remove a serious defeater. If a camera lens may be damaged, photographs from that camera are not enough to settle the matter. We should seek another device, another sense, or a publicly checkable method. The goal is not an impossible view from nowhere, but greater independence among the strands of evidence.
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