The more extensive a man's knowledge of what has been done, the greater will be his power of knowing what to do.

The reward of one duty is the power to fulfill another.

When it is not in our power to follow what is true, we ought to follow what is most probable.

The strength and power of a country depends absolutely on the quantity of good men and women in it.

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.