Though he died too young, Carl Sagan left behind an impressively large body of work, including more than 600 scientific papers and more than 20 books. Of those books, none is more widely known to the public — or, still, more widely read by the public — than Cosmos, accompanied as it was by Cosmos: A Personal Voyage, a companion television series on PBS. Sagan’s other popular books, like Shadows of Forgotten Ancestors or Contact (the basis of the 1997 Hollywood movie) are also well worth reading, but we perhaps ignore at our greatest peril The Demon-Haunted World: Science as a Candle in the Dark. Published in 1995, the year before Sagan’s death, it stands as his testament to the importance of critical, scientific thinking for all of us.
The Demon-Haunted World is the subject of the Genetically Modified Skeptic video above, whose host Drew McCoy describes it as his favorite book. He pays special attention to its chapter in which Sagan lays out what he calls his “baloney detection kit.” This assembled metaphorical box of tools for diagnosing fraudulent arguments and constructing reasoned ones involves these nine principles:
Wherever possible there must be independent confirmation of the “facts.”
Encourage substantive debate on the evidence by knowledgeable proponents of all points of view.
Arguments from authority carry little weight — “authorities” have made mistakes in the past. They will do so again in the future. Perhaps a better way to say it is that in science there are no authorities; at most, there are experts.
Spin more than one hypothesis. If there’s something to be explained, think of all the different ways in which it could be explained. Then think of tests by which you might systematically disprove each of the alternatives.
Try not to get overly attached to a hypothesis just because it’s yours. It’s only a way station in the pursuit of knowledge. Ask yourself why you like the idea. Compare it fairly with the alternatives.
See if you can find reasons for rejecting it. If you don’t, others will.
If whatever it is you’re explaining has some measure, some numerical quantity attached to it, you’ll be much better able to discriminate among competing hypotheses. What is vague and qualitative is open to many explanations.
If there’s a chain of argument, every link in the chain must work (including the premise) — not just most of them.
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