- A philosopher may try to prove the truth of something he believed before he was a philosopher, but even if he succeeds, his belief never regain the untroubled character, and the settled place in his mind, which it had at first.
- The Rationality of Induction, Oxford: Clarendon, 1986. Page 99, first paragraph.
- If a lack of empirical foundations is a defect of the theory of logical probability, it is also a defect of deductive logic.
- The Rationality of Induction, Oxford: Clarendon, 1986. Page 176, last paragraph.