Chapter 5, Mathematical Certainty and Reductio ad Absurdum, part 2

Therefore, when they begin to see looming ahead some such ridiculous result as 2 + 3 = 7, they shrink into themselves and try to find some process of twisting the logic, and tinkering the equation, which will make the answer come out a truism instead of an absurdity; and then they say, “Our hypothetical premiss is most likely true because the conclusion to which it brings us is obviously and indisputably true.” If anyone points out that there seems to be a flaw in the argument, they say, “You cannot expect to get mathematical certainty in this world,” or “You must not push logic too far,” or “Everything is more or less compromise,” and so on.

Of course, there is no mathematical certainty to be had on those terms. You could have no mathematical certainty about the amount you owed your grocer if you tinkered the process of adding up his bill. I wish to call your attention to the fact that even in this world there is a good deal of mathematical certainty to be had by whosoever has endless patience, scrupulous accuracy in stating his own ignorance, reverence for the As-Yet-Unknown, and perfect fearlessness in meeting the reductio ad absurdum.