I’ve been writing about and teaching critical thinking for more than two decades. “Form beliefs on the basis of the evidence,” was my mantra, and I taught tens of thousands of students how to do just that. Why, then did people leave my classroom with the same preposterous beliefs as when they entered—from alternative medicine to alien abductions to Obama being a Muslim? Because I had been doing it wrong.

The problem is that everyone thinks they form their beliefs on the basis of evidence. That’s one of the issues, for example, with fake news. Whether it’s Facebook, Twitter, or just surfing Google, people read and share stories either that they want to believe or that comport with what they already believe—then they point to those stories as evidence for their beliefs. Beliefs are used as evidence for beliefs, with fake news just providing fodder.

Teaching people to formulate beliefs on the basis of evidence may, ironically, trap them in false views of reality. Doing so increases their confidence in the truth of a belief because they think they’re believing as good critical thinkers would, but they’re actually digging themselves into a cognitive sinkhole. The more intelligent one is, the deeper the hole. As Michael Shermer famously stated, “Smarter people are better at rationalizing bad ideas.” That is, smarter people are better at making inferences and using data to support their belief, independent of the truth of that belief.

What, then, can we skeptics do? Here’s my recommendation: Instead of telling people to form beliefs on the basis of evidence, encourage them to seek out something, anything, that could potentially undermine their confidence in a particular belief. (Not something that will, but something that could. Phrased this way it’s less threatening.) This makes thinking critical.

Here’s an example of how to accomplish that: Jessica believes Obama is a Muslim. Ask her, on a scale from 1–10, how confident she is in that belief. Once she’s articulated a number, say 9, ask her what evidence she could encounter that would undermine her confidence. For example, what would it take to lower her confidence from 9 to 8, or even 6? Ask her a few questions to help her clarify her thoughts, and then invite her to seek out that evidence.

Philosophers call this process “defeasibility”. Defeasibility basically refers to whether or not a belief is revisable. For example, as Muslims don’t drink alcohol, perhaps a picture of Obama drinking beer would lower her confidence from 9 to 8, or maybe videos over the last eight years of Obama praying at Saint John’s Church in DC would be more effective, lowering her confidence to a 6. Or maybe these wouldn’t budge her confidence. Maybe she’d have well-rehearsed, uncritical responses to these challenges.

This is exactly what happened in my Science and Pseudoscience class at Portland State University. A student insisted Obama was a Muslim. When I displayed a series of pictures of Obama drinking beer on the projector, he instantly and emphatically responded,“Those pictures are photoshopped!” I asked him, on a scale of 1–10, how sure he was. He responded 9.9. I then asked him if he’d like to write an extra-credit paper detailing how the claim that the pictures were photoshopped could be false.

This strategy is effective because asking the question, “What evidence would it take to change your mind?” creates openings or spaces in someone’s belief where they challenge themselves to reflect upon whether or not their confidence in a belief is justified. You’re not telling them anything. You’re simply asking questions. And every time you ask it’s another opportunity for people to reevaluate and revise their beliefs. Every claim can be viewed as such, an opportunity to habituate people to seek disconfirming evidence.

If we don’t place defeasibility front and center, we’re jeopardizing peoples’ epistemic situation by unwittingly helping them artificially inflate the confidence they place in their beliefs. We’re creating less humility because they’re convincing themselves they’re responsible believers and thus that their beliefs are more likely to be true. That’s the pedagogical solution. It’s the easy part.

The more difficult part is publicly saying, “I don’t know” when we’re asked a question and don’t know the answer. And more difficult still, admitting “I was wrong” when we make a mistake. These are skills worth practicing.

Critical thinking begins with the assumption that our beliefs could be in error, and if they are, that we will revise them accordingly. This is what it means to be humble. Contributing to a culture where humility is the norm begins with us. We can’t expect people to become critical thinkers until we admit our own beliefs or reasoning processes are sometimes wrong, and that there are some questions, particularly in our specialties, that we don’t know how to answer. Doing so should help people become better critical thinkers, far more than 1000 repetitions of “form beliefs on the basis of evidence” ever could.

About the Author

Peter Boghossian is an Assistant Professor of Philosophy at Portland State University and an affiliated faculty member at Oregon Health Science University in the Division of General Internal Medicine. His popular pieces can be found in Scientific American, Time, the Philosopher’s Magazine, and elsewhere. Follow Peter on Twitter @peterboghossian.

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