The fact is the human race is not only slow about borrowing valuable ideas--it sometimes persists in not borrowing them at all.
- "Some National Stupidities"

The man with a new idea is a Crank until the idea succeeds.
- Following the Equator

It always happens that when a man seizes upon a neglected and important idea, people inflamed with the same notion crop up all around.
- Life on the Mississippi

You've got to admire men that deal in ideas of that size and can tote them around without crutches.
- Life on the Mississippi

The king looked puzzled--he wasn't a very heavy weight, intellectually. His head was an hour-glass; it could stow an idea, but it had to do it a grain at a time, not the whole idea at once.
- A Connecticut Yankee in King Arthur's Court