How Can We Know What is True? And What Is BS? Tips from Carl Sagan, Richard Feynman & Michael Shermer

Sci­ence denial­ism may be a deeply entrenched and enor­mous­ly dam­ag­ing polit­i­cal phe­nom­e­non. But it is not a whol­ly prac­ti­cal one, or we would see many more peo­ple aban­don med­ical sci­ence, air trav­el, com­put­er tech­nol­o­gy, etc. Most of us tac­it­ly agree that we know cer­tain truths about the world—gravitational force, nav­i­ga­tion­al tech­nol­o­gy, the germ the­o­ry of dis­ease, for exam­ple. How do we acquire such knowl­edge, and how do we use the same method to test and eval­u­ate the many new claims we’re bom­bard­ed with dai­ly?

The prob­lem, many pro­fes­sion­al skep­tics would say, is that we’re large­ly unaware of the epis­temic cri­te­ria for our think­ing. We believe some ideas and doubt oth­ers for a host of rea­sons, many of them hav­ing noth­ing to do with stan­dards of rea­son and evi­dence sci­en­tists strive towards. Many pro­fes­sion­al skep­tics even have the humil­i­ty to admit that skep­tics can be as prone to irra­tional­i­ty and cog­ni­tive bias­es as any­one else.

Carl Sagan had a good deal of patience with unrea­son, at least in his writ­ing and tele­vi­sion work, which exhibits so much rhetor­i­cal bril­liance and depth of feel­ing that he might have been a poet in anoth­er life. His style and per­son­al­i­ty made him a very effec­tive sci­ence com­mu­ni­ca­tor. But what he called his “Baloney Detec­tion Kit,” a set of “tools for skep­ti­cal think­ing,” is not at all unique to him. Sagan’s prin­ci­ples agree with those of all pro­po­nents of log­ic and the sci­en­tif­ic method. You can read just a few of his pre­scrip­tions below, and a full unabridged list here.

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.

Anoth­er skep­tic, founder and edi­tor of Skep­tic mag­a­zine Michael Sher­mer, sur­rounds his epis­te­mol­o­gy with a sym­pa­thet­ic neu­ro­science frame. We’re all prone to “believ­ing weird things,” as he puts it in his book Why Peo­ple Believe Weird Things and his short video above, where he intro­duces, fol­low­ing Sagan, his own “Baloney Detec­tion Kit.” The human brain, he explains, evolved to see pat­terns every­where as a mat­ter of sur­vival. All of our brains do it, and we all get a lot of false pos­i­tives.

Many of those false pos­i­tives become wide­spread cul­tur­al beliefs. Sher­mer him­self has been accused of insen­si­tive cul­tur­al bias (evi­dent in the begin­ning of his video), intel­lec­tu­al arro­gance, and worse. But he admits up front that sci­en­tif­ic think­ing should tran­scend indi­vid­ual per­son­al­i­ties, includ­ing his own. “You shouldn’t believe any­body based on author­i­ty or what­ev­er posi­tion they might have,” he says. “You should check it out your­self.”

Some of the ways to do so when we encounter new ideas involve ask­ing “How reli­able is the source of the claim?” and “Have the claims been ver­i­fied by some­body else?” Return­ing to Sagan’s work, Sher­mer offers an exam­ple of con­trast­ing sci­en­tif­ic and pseu­do­sci­en­tif­ic approaches—the SETI (Search for Extrater­res­tri­al Intel­li­gence) Insti­tute and UFO believ­ers. The lat­ter, he says, uncrit­i­cal­ly seek out con­fir­ma­tion for their beliefs, where the sci­en­tists at SETI rig­or­ous­ly try to dis­prove hypothe­ses in order to rule out false claims.

Yet it remains the case that many people—and not all of them in good faith—think they’re using sci­ence when they aren’t. Anoth­er pop­u­lar sci­ence com­mu­ni­ca­tor, physi­cist Richard Feyn­man, rec­om­mend­ed one method for test­ing whether we real­ly under­stand a con­cept or whether we’re just repeat­ing some­thing that sounds smart but makes no log­i­cal sense, what Feyn­man calls “a mys­tic for­mu­la for answer­ing ques­tions.” Can a con­cept be explained in plain Eng­lish, with­out any tech­ni­cal jar­gon? Can we ask ques­tions about it and make direct obser­va­tions that con­firm or dis­con­firm its claims?

Feyn­man was espe­cial­ly sen­si­tive to what he called “intel­lec­tu­al tyran­ny in the name of sci­ence.” And he rec­og­nized that turn­ing forms of know­ing into emp­ty rit­u­als result­ed in pseu­do­sci­en­tif­ic think­ing. In a won­der­ful­ly ram­bling, infor­mal, and auto­bi­o­graph­i­cal speech he gave in 1966 to a meet­ing of the Nation­al Sci­ence Teach­ers Asso­ci­a­tion, Feyn­man con­clud­ed that think­ing sci­en­tif­i­cal­ly as a prac­tice requires skep­ti­cism of sci­ence as an insti­tu­tion.

“Sci­ence is the belief in the igno­rance of experts,” says Feyn­man. “If they say to you, ‘Sci­ence has shown such and such,’ you might ask, ‘How does sci­ence show it? How did the sci­en­tists find out? How? What? Where?’” Ask­ing such ques­tions does not mean we should reject sci­en­tif­ic con­clu­sions because they con­flict with cher­ished beliefs, but rather that we should­n’t take even sci­en­tif­ic claims on faith.

For elab­o­ra­tion on Sher­mer, Sagan and Feyn­man’s approach­es to telling good sci­en­tif­ic think­ing from bad, read these arti­cles in our archive:

Carl Sagan Presents His “Baloney Detec­tion Kit”: 8 Tools for Skep­ti­cal Think­ing

Richard Feyn­man Cre­ates a Sim­ple Method for Telling Sci­ence From Pseu­do­science (1966)

Richard Feynman’s “Note­book Tech­nique” Will Help You Learn Any Subject–at School, at Work, or in Life

Michael Shermer’s Baloney Detec­tion Kit: What to Ask Before Believ­ing


Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness

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  • Jan says:

    I like the bit around the one minute mark with the danc­ing indi­ans and mr sher­mer talks about super­sti­tion. I believe I may even see a pat­tern there, but that may just be me.

  • Ben David says:


    It’s the Glob­al warm­ing *skep­tics* that are fid­dling with the data?
    And the “sci­ence is set­tled” — rather than cit­ing that issue as an exam­ple of ongo­ing sci­en­tif­ic debate?

    Stopped watch­ing right there…

  • jkop says:

    It’s not just “danc­ing indi­ans” but a dance rit­u­al which is an exam­ple of human super­sti­tion. Note that Sher­mer talks of human super­sti­tion (not super­sti­tious danc­ing indi­ans).

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