Ignorance, the root and stem of all evil.

Think good, and good follows. Think evil, and evil follows. You are what you think all day long.

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.

I am not an Athenian or a Greek, but a citizen of the world.

Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.

Death may be the greatest of all human blessings.

The most important knowledge is that which guides the way you lead your life.

An honest man is always a child.

If you can't explain it to a six year old, you don't understand it yourself.