The sentiments of an adult are compounded of a kernel of instinct surrounded by a vast husk of education.

Morality in sexual relations, when it is free from superstition, consists essentially in respect for the other person, and unwillingness to use that person solely as a means of personal gratification, without regard to his or her desires.

The human race may well become extinct before the end of the century.

The first man who said "fire burns" was employing scientific method, at any rate if he had allowed himself to be burnt several times. This man had already passed through the two stages of observation and generalization. He had not, however, what scientific technique demands - a careful choice of significant facts on the one hand, and, on the other hand, various means of arriving at laws otherwise than my mere generalization.

Pure mathematics consists entirely of assertions to the effect that, if such and such a proposition is true of anything, then suchand such another proposition is true of that thing.... Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true.

None but a coward dares to boast that he has never known fear.

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.