Civilization advances by extending the number of important operations which we can perform without thinking about them. Operations of thought are cavalry charges in a battle - they are limited in number, they require fresh horses, and must only be made at decisive moments.

Ideas won't keep. Something must be done about them.

The world is shocked, or amused, by the sight of saintly old people hindering in the name of morality the removal of obvious brutalities from a legal system.

There are no whole truths: all truths are half-truths. It is trying to treat them as whole truths that plays to the devil.

By relieving the brain of all unnecessary work, a good notation sets it free to concentrate on more advanced problems, and in effect increases the mental power of the race.

One main factor in the upward trend of animal life has been the power of wandering.

Learning preserves the errors of the past as well as its wisdom.