“Some care is needed in using Descartes' argument. "I think, therefore I am" says rather more than is strictly certain. It might seem as though we are quite sure of being the same person to-day as we were yesterday, and this is no doubt true in some sense. But the real Self is as hard to arrive at as the real table, and does not seem to have that absolute, convincing certainty that belongs to particular experiences.”

“The battle must be fought exactly as the battle of religious toleration was fought. And as in that case, so in this, a decay in the intensity of belief is likely to prove the decisive factor. While men were convinced of the absolute truth of Catholicism or Protestantism, as the case may be, they were willing to persecute on account of them. While men are quite certain of their modern creeds, they will persecute on their behalf. Some element of doubt is essential to the practice, thought not to the theory, of toleration.”

“The true spirit of delight, the exaltation, the sense of being more than Man, which is the touchstone of the highest excellence, is to be found in mathematics as surely as in poetry.”

“I think we ought always to entertain our opinions with some measure of doubt. I shouldn't wish people dogmatically to believe any philosophy, not even mine. ”

“I am myself a dissenter from all known religions, and I hope that every kind of religious belief will die out. I do not believe that, on the balance, religious belief has been a force for good. Although I am prepared to admit that in certain times and places it has had some good effects, I regard it as belonging to the infancy of human reason, and to a stage of development which we are now outgrowing.”

“The true function of logic ... as applied to matters of experience ... is analytic rather than constructive; taken a priori, it shows the possibility of hitherto unsuspected alternatives more often than the impossibility of alternatives which seemed prima facie possible. Thus, while it liberates imagination as to what the world may be, it refuses to legislate as to what the world is”

“Dogmatism and skepticism are both, in a sense, absolute philosophies; one is certain of knowing, the other of not knowing. What philosophy should dissipate is certainty, whether of knowledge or ignorance.”