Swinburne and Plantinga on internal rationality

Abstract

Plantinga defines S's belief as ‘privately rational if and only if it is probable on S's evidence’, and ‘publicly rational if and only if it is probable with respect to public evidence’, and he claims that ‘it is an immediate consequence of these definitions that all my basic beliefs are privately rational’. I made it explicitly clear in my review that on my account of a person's evidence (quoted and used by Plantinga) as ‘the content of his basic beliefs (weighted by his degree of confidence in them)’, that is not the case. I emphasize ‘weighted by his degree of confidence in them’. I wrote explicitly: ‘for more or less any belief, however convinced you are of it initially, other evidence of which you are equally convinced could rend it overall improbable’. Put technically, in probabilistic terms, basic beliefs come to us with different degrees of prior probability varying with our degree of confidence in them, but a belief with a high prior probability can in the light of other beliefs of our current set have a lower posterior probability. If you continue to hold on to a basic belief when its probability on the total evidence is below half, that belief is not privately rational.