Carl Sagan

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

Except in pure mathematics, nothing is known for certain (although much is certainly false).

We began as wanderers, and we are wanderers still.

We on Earth have just awakened to the great oceans of space and time from which we have emerged. We are the legacy of 15 billion years of cosmic evolution. We have a choice: We can enhance life and come to know the universe that made us, or we can squander our 15 billion-year heritage in meaningless self-destruction. What happens in the first second of the next cosmic year depends on what we do, here and now, with our intelligence and our knowledge of the cosmos.

When a honeybee dies it releases a death pheromone, a characteristic odour that signals the survivors to remove it from the hive. The corpse is promptly pushed and tugged out of the hive. The death pheromone is oleic acid. What happens if a live bee is dabbed with a drop of oleic acid? Then no matter how strapping and vigourous it might be, it is carried kicking and screaming out of the hive.

But down deep, at the molecular heart of life we're essentially identical to trees.

We are a way of the universe knowing itself.

Absolute certainty will always elude us. We will always be mired in error. The most each generation can hope for is to reduce the error. . . .

When you look more generally at life on Earth, you find that it is all the same kind of life. There are not many different kinds; there's only one kind. It uses about fifty fundamental biological building blocks, organic molecules.

If we are not able to ask skeptical questions, to interrogate those who tell us that something is true, to be skeptical of those in authority, then, we are up for grabs for the next charlatan (political or religious) who comes rambling along.

All inquires carry with them some element of risk. There is no guarantee that the universe will conform to our predispositions.

A still more glorious dawn awaits / not a sunrise, but a galaxy-rise / a morning filled with 400 billion suns / the rising of the milky way

I think the health of our civilization, the depth of our awareness about the underpinnings of our culture, and our concern for the future, can all be tested by how well we support our libraries.

Stars are phoenixes, rising from their own ashes.

The understanding of the intent of the artist which I can achieve when high sometimes carries over to when I’m down. This is one of many human frontiers which cannabis has helped me traverse.

Some 5 billion years from now, there will be a last perfect day on Earth... then the sun will begin to die, life will be extinguished, the oceans will boil and evaporate away.

Otherwise we don't run the government the government runs us

It's perilous and foolhardy for the average citizen to remain ignorant about global warming, say, or ozone depletion, air pollution, toxic and radioactive wastes, acid rain, topsoil erosion, tropical deforestation, exponential population growth. Jobs and wages depend on science and technology.

Other things being equal, it is better to be smart than to be stupid.

I set before you two ways: You can use your technology to destroy yourselves or to carry you to the planets and the stars. It's up to you.

After I give lectures-on almost any subject-I am often asked, "Do you believe in UFOs?" I'm always struck by how the question is phrased, the suggestion that this is a matter of belief and not evidence. I'm almost never asked, "How good is the evidence that UFOs are alien spaceships?"