The quarrels of theologians and philosophers have not been about religion, but about philosophy; and philosophers not unfrequently seem to entertain the same feeling toward theologians that sportsmen cherish toward poachers.

The population question is the real riddle of the sphinx, to which no political Oedipus has as yet found the answer. In view of the ravages of the terrible monster over-multiplication, all other riddle sink into insignificance.

And you very soon find out, if you have not found it out before, that patience and tenacity of purpose are worth more than twice their weight of cleverness.

The rules of the game are what we call the laws of nature.

In matters of intellect, follow your reason as far as it will take you, without regard for any other consideration.

In the world of letters, learning and knowledge are one, and books are the source of both; whereas in science, as in life, learning and knowledge are distinct, and the study of things, and not of books, is the source of the latter.

Mathematics may be compared to a mill of exquisite workmanship, which grinds your stuff to any degree of fineness.