Carl Sagan
Astronomer & Science Communicator · 1934–1996
Carl Sagan was an American astronomer, cosmologist, and one of the greatest science communicators who ever lived. As a professor at Cornell University and host of the groundbreaking television series Cosmos, he brought the wonder of the universe into millions of living rooms — and made the case that science is not just useful but beautiful.
Sagan was not an aggressive critic of religion in the way the New Atheists would later become, but he was a firm sceptic. He believed that extraordinary claims require extraordinary evidence, and that superstition and pseudoscience — including religious dogma — erode our ability to think clearly about the world.
Extraordinary claims require extraordinary evidence
Sagan's most lasting contribution to popular epistemology. The principle applies equally to UFOs, pseudoscience, and religious claims — and became a cornerstone of the sceptical movement.
The baloney detection kit
Sagan outlined a practical toolkit for identifying faulty reasoning: look for independent confirmation, encourage debate, ask if the claim can be falsified, check for alternative explanations. Tools for any citizen, not just scientists.
Science and wonder are not in tension
Against the idea that science strips the world of meaning, Sagan argued that understanding the actual scale and age and complexity of the universe produces a deeper awe than any myth could.
Scepticism is a civic duty
A democracy requires citizens who can think critically about what they're told. When people can't evaluate evidence, they become vulnerable to demagogues, charlatans, and institutions with interests in their ignorance.
Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every 'superstar,' every 'supreme leader,' every saint and sinner in the history of our species lived there — on a mote of dust suspended in a sunbeam.
The Demon-Haunted World
His 1995 book The Demon-Haunted World: Science as a Candle in the Dark is a passionate defence of scientific thinking and sceptical inquiry. Sagan argues that in a world full of superstition, pseudoscience, and unchecked belief, the scientific method is our best tool for finding truth. The book has aged beautifully and reads as urgently today as when it was written.
Essential books
Best quotes
“Extraordinary claims require extraordinary evidence.”
“The cosmos is within us. We are made of star-stuff. We are a way for the universe to know itself.”
“We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology.”
“Science is not only compatible with spirituality; it is a profound source of spirituality.”
“One of the saddest lessons of history is this: if we've been bamboozled long enough, we tend to reject any evidence of the bamboozle. We're no longer interested in finding out the truth.”
“For me, it is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring.”
Legacy
Sagan died in 1996, but his influence only grows. Cosmos was rebooted by Neil deGrasse Tyson in 2014, and The Demon-Haunted Worldis regularly cited by scientists, educators, and sceptics as one of the most important books on critical thinking ever written. His famous line — “extraordinary claims require extraordinary evidence” — has become a foundational principle of the sceptical movement.
Continue exploring
Richard Dawkins
Evolutionary biologist, author of The God Delusion.
Christopher Hitchens
Author of God Is Not Great.
Recommended reading
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The fine-tuning argument
The fine-tuning argument — is the universe calibrated for life?