Love is something far more than desire for sexual intercourse; it is the principal means of escape from the loneliness which afflicts most men and women throughout the greater part of their lives.

Right discipline consists, not in external compulsion, but in the habits of mind which lead spontaneously to desirable rather than undesirable activities.

It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition.

Do not feel envious of the happiness of those who live in a fool's paradise, for only a fool will think that is happiness.

The greatest challenge to any thinker is stating the problem in a way that will allow a solution.

No man is liberated from fear who dare not see his place in the world as it is; no man can achieve the greatness of which he is capable until he has allowed himself to see his own littleness.

Is there any knowledge in the world which is so certain that no reasonable man could doubt it?