The greatest productive force is human selfishness.

You can have peace. Or you can have freedom. Don't ever count on having both at once.

Sense is never common.

I'll give you an exact definition. When the happiness of another person becomes as essential to yourself as your own, then the state of love exists.

Duty is a debt you owe to yourself to fulfill obligations you have assumed voluntarily.

Progress isn't made by early risers. It's made by lazy men trying to find easier ways to do something.

Since survival is the sine qua non, I now define the "moral behavior" as "behavior that tends toward survival".