Following Alvin Platinga, Richard Foley summarizes the principles of Locke’s epistemology in three principles (Intellectual Trust in Oneself and Others): Evidence (the “obligation to base one’s opinion on one’s evidence,” the latter defined as “what one knows with certainty”); appraisal (the obligation “to appraise the probability of propositions on one’s evidence”); and proportionality (the obligation to “adopt degrees of confidence . . . proportionate to their probabilities on one’s evidence”) (89-90).
To be sure, there is much to be said for Locke’s criteria, but Foley claims that they are based on largely unexamined premises: “First, there is his optimism: if individuals use their intellectual equipment well, following the above principles
of evidence and proportionality, they can expect to have accurate opinions. Second, there is his individualism: his principles require individuals
to exercise their own judgment about how strongly their evidence
supports other propositions. Finally, there is his egalitarianism: his principles are intended for everyone, not just the intellectually elite” (90).
Foley acknowledges that Locke shows some awareness of the complications of these premises, but he is also deeply hostile to reliance on the opinions of others. Locke writes: “For, I think, we may as rationally hope to see with other Mens Eyes, as to know by other Mens Understandings. So much as we our selves consider and comprehend of Truth and Reason, so much we possess of real and true Knowledge. The floating of other Mens Opinions in our brains makes us not one jot the more knowing, though they happen to be true. What in them was science, is in us but Opiniatretry, whilst we give up our Assent only to reverend names, and do not, as they did, employ our own Reason to understand those Truths, which gave them reputation. . . . In the Sciences, every one has so much, as he really knows and comprehends: What he believes only, and takes upon trust, are but shreds; which however well in the whole piece, make no considerable addition to his stock, who gathers them. Such borrowed Wealth, like Fairy- money, though it were Gold in the hand from he who received it, will be but Leaves and Dust when it comes to use” (quoted 91).
Instead, everyone, no matter how unschooled, should “rely on their own judgment and reason (his individualism), and if they are careful to conform to their opinions to the evidence, the result will be ‘real and true knowledge’ (his optimism)” (91).