The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals.

Action is the catalyst that creates accomplishments. It is the path that takes us from uncrafted hopes to realized dreams.

Some experience of popular lecturing had convinced me that the necessity of making things plain to uninstructed people, was one of the very best means of clearing up the obscure corners in one's own mind.

The supernatural is being swept out of the universe in the flood of new knowledge of what is natural. It will soon be as impossible for an intelligent, educated man or woman to believe in a god as it is now to believe that earth is flat, that flies can be spontaneously generated, that disease is a divine punishment, or that death is always due to witchcraft.

A well-worn adage advises those who set out upon a great enterprise to count the cost, yet some of the greatest enterprises have succeeded because the people who undertook them did not count the cost.

Protoplasm, simple or nucleated, is the formal basis of all life. It is the clay of the potter: which, bake it and paint it as hewill, remains clay, separated by artifice, and not by nature from the commonest brick or sun-dried clod.

What are the moral convictions most fondly held by barbarous and semi-barbarous people? They are the convictions that authority is the soundest basis of belief; that merit attaches to readiness to believe; that the doubting disposition is a bad one, and skepticism is a sin.