A blade of grass is a commonplace on Earth; it would be a miracle on Mars. Our descendants on Mars will know the value of a patch of green. And if a blade of grass is priceless, what is the value of a human being?

— Carl Sagan

A book is made from a tree. It is an assemblage of flat, flexible parts (still called "leaves") imprinted with dark pigmented squiggles. One glance at it, and you hear the voice of another person, perhaps someone dead for thousands of years. Across the millennia, the author is speaking, clearly and silently, inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people, citizens of distant epochs, who never knew one another. Books break the shackles of time ― proof that humans can work magic.

— Carl Sagan

A celibate clergy is an especially good idea, because it tends to suppress any hereditary propensity toward fanaticism.

— Carl Sagan

Across the sea of space, the stars are other suns.

— Carl Sagan

Adolf Hitler! Ken, it makes me furious. Forty million people die to defeat that megalomaniac, and he's the star of the first broadcast to another civilization? He's representing us. And them. It's that madman's dream come true.

— Carl Sagan

Advances in medicine and agriculture have saved vastly more lives than have been lost in all the wars in history.

— Carl Sagan

Advertising teaches people not to trust their judgment. Advertising teaches people to be stupid.

— Carl Sagan

A galaxy is composed of gas and dust and stars - billions upon billions of stars. Every star may be a sun to someone.

— Carl Sagan

All her life, dreams had been her friends. Her dreams were unusually detailed, well-structured, colorful.

— Carl Sagan

All of us cherish our beliefs. They are, to a degree, self-defining. When someone comes along who challenges our belief system as insufficiently well based - or who, like Socrates, merely asks embarrassing questions that we haven't thought of, or demonstrates that we've swept key underlying assumptions under the rug - it becomes much more than a search for knowledge. It feels like a personal assault.

— Carl Sagan