So far I have been speaking of theoretical science, which is an attempt to understand the world. Practical science, which is an attempt to change the world, has been important from the first, and has continually increased in importance, until it has almost ousted theoretical science from men's thoughts.

Whoever wishes to become a philosopher must learn not to be frightened by absurdities.

Science may set limits to knowledge, but should not set limits to imagination.

Of all forms of caution, caution in love is perhaps the most fatal to true happiness.

Is the set of all sets which are not members of themselves a member of itself?

Worry is a form of fear.

The desire for legitimate offspring is, in fact, according to the Catholic Church, the only motive which can justify sexual intercourse.