But as the work proceeded I was continually reminded of the fable about the elephant and the tortoise. Having constructed an elephant upon which the mathematical world could rest, I found the elephant tottering, and proceeded to construct a tortoise to keep the elephant from falling. But the tortoise was not more secure than the elephant, and after some twenty years of very arduous toil, I came to the conclusion that there was nothing more that I could do in the way of making mathematical knowledge indubitable.

What makes a free thinker is not his beliefs, but the way in which he holds them. If he holds them because his elders told him they were true when he was young, or if he holds them because if he did not he would be unhappy, his thought is not free; but if he holds them because, after careful thought, he finds a balance in their favor, then his thought is free, however odd his conclusions may seem.

Inferences of Science and Common Sense differ from those of deductive logic and mathematics in a very important respect, namely, when the premises are true and the reasoning correct, the conclusion is only probable.

Animal rights, taken to their logical conclusion, mean votes for oysters.

The chicken noticed that the farmer came every day to feed it. It predicted that the farmer would continue to bring food every day. Inductivists think that the chicken had "extrapolated" its observations into a theory, and that each feeding time added justification to that theory. Then one day the farmer came and wrung the chicken's neck. This inductively justifies the conclusion that induction cannot justify any conclusion.