In Mind, Brain, and Free Will, Richard Swinburne states the Principle of Credulity (hereafter, PC) is,
“a fundamental a priori epistemic principle…that any basic belief is probably true on the believer’s evidence that he believes it – in the absence of evidence in the form of other basic beliefs of that believer which makes it probably that he is mistaken.”1
This means that what seems to be true is probably true. Swinburne endorses this a fundamental epistemic principle to avoid extreme skepticism (extreme skepticism meaning that most of our ordinary beliefs are not probably true). However, Swinburne does not motivate PC other than giving a dilemma between endorsing PC or extreme skepticism and does not give any reason to suppose all other solutions fail, strong foundationalism, coherentism, or externalism.2 In part this is because Swinburne believes that the debate between externalism and internalism is simply a dispute about words.3 Most, including myself, believe the externalism/internalism controversies is more than a dispute about words. Lastly, there seems to be an inexplicit notion that memory belief(s) can only be justified if PC is accepted and that if memory belief(s) are not justified then not many of our ordinary beliefs are. If memory beliefs can only be justified through PC, then this is motivation for accepting it. However, there are a couple of problems with Swinburne’s version of PC.
Other than the problem already noted that Swinburne does not give explicit reasons why any position would lead to extreme skepticism, he also does not give any good ground to think PC is in fact truth conducive. Most philosophers tend to agree that just because skeptical scenarios could be true, that does not mean they are likely.
If skeptical scenarios are true, then we would not be able to see defeaters from our vantage point. Take this example, if we are really in a matrix pod there is no way of seeing that is so. There could never be any defeaters in such a world and all our perceptual knowledge would be false. More importantly, as epistemologists we should not rule out extreme skepticism simply because it is unappealing, since it may be our current predicament. To respond to the skeptical worry with PC when PC is motivated by avoiding skepticism is question begging.
Despite Swinburne’s version of PC being unmotivated and unconvincing there is a more suitable version of it, PC*; that what appears to be the case is rational to hold unless there is evidence against the prima fascia belief. I believe this is a common sense version of PC. If I think I see a chair in the corner of my room then I am rational to believe there is a chair there unless I have stronger evidence against the belief. Stronger evidence against the belief would be trying to feel it and see my hand go right through where the chair is supposed to be, thus now it is rational to believe it is a hologram. The strength of PC* is that it allows skepticism to be possibly right, does not claim to be truth conducive, but still gives guidance towards rational inquiry. If we are not in the skeptical position, then PC* is likely to be truth conducive as well.
1. Swinburne: Mind, Brain, Free Will, p. 42 (2013)
2. Ibid., p. 44
3. Ibid., p 40