Critical thinking is the habit of judging information carefully before you decide what to believe or do. In practice it comes down to one question you ask yourself: “How do I actually know that?” It sounds simple, and yet most of us were never taught it.
I was reminded of this by Joe Rogan, the American comedian who became one of the most listened-to interviewers on the internet. In a January 2019 episode with the psychologist Jonathan Haidt, co-author of The Coddling of the American Mind, the talk turned to school. As I remember it, Rogan said he wished someone had taught him critical thinking and asked why nobody had. Haidt’s answer was that American schools had tried, and nobody had found a method that reliably worked.
Nobody taught me critical thinking at school either. I was taught a great deal about what to think. Since school let us down, here is what critical thinking is, where it came from, and how to practice it on an ordinary Tuesday.
What is critical thinking?
The shortest useful definition comes from the American philosopher Robert Ennis: critical thinking is reasonable, reflective thinking aimed at deciding what to believe or do. Wikipedia describes it as analyzing the available facts, evidence, observations and arguments in order to reach sound conclusions or informed choices.
My version, for those of us without a philosophy degree: critical thinking is the habit of checking how you know what you know.
When I first wrote about this in 2019, I said the key was objectivity, meaning thought free of prejudice, convictions and beliefs. Today I would put it more carefully. Nobody is fully objective, and nobody thinks without beliefs. We accept certain truths easily and then build further conclusions on top of them. What if those truths are wrong? Critical thinking means taking your beliefs out of the closet every so often and checking whether the moths have got to them.
What critical thinking is not
- Fault-finding. Complaining about everything says more about your mood than about your analysis.
- Cynicism. “Everybody lies” is as lazy a conclusion as “everybody tells the truth”.
- Contrarianism. “I don’t trust the media, I trust YouTube videos” just swaps one authority for another.
- Winning arguments. The goal is to get to the truth, even when the truth is inconvenient and you lose the argument.
That goes for a magazine called Mr Heretic, too. The word comes from the Greek hairesis, which originally meant “choice”. A heretic in that old sense doesn’t disagree with everybody. He insists on choosing for himself, and he checks before he chooses.
Where did it come from? From Socrates to Kahneman
Critical thinking goes back to Socrates, who lived in Athens in the fifth century BC and was famous for asking awkward questions of people with a reputation for wisdom. Their knowledge often failed to survive a few persistent “why?“s. So we have had the method for more than two thousand years and still rarely use it, which says something about human nature on its own.
In the 20th century the American philosopher John Dewey turned the idea into an educational goal, though he usually called it “reflective thinking”. The person who explained best why critical thinking comes so hard to us was the psychologist Daniel Kahneman, who won the Nobel Prize in economics in 2002. In Thinking, Fast and Slow (2011) he described two modes of the mind:
| System 1 | System 2 | |
|---|---|---|
| How it works | fast, automatic, effortless | slow, deliberate, effortful |
| What it’s good for | everyday decisions, recognizing faces, driving a familiar route | arithmetic, analysis, checking arguments |
| Weakness | mental shortcuts and cognitive biases | it’s lazy, so it gladly hands the wheel to System 1 |
In practice, critical thinking is noticing when you need to wake System 2 up before System 1 hits “share”.
Kahneman himself supplied the best footnote. One chapter of his book rested on studies of behavioral priming (tiny cues supposedly steering what we do) that have since struggled to replicate. When a 2017 analysis showed how weak those studies were, he replied: “I placed too much faith in underpowered studies.” His first paper with Amos Tversky, he noted, had been about exactly that mistake. Anyone can fall for a bias. Admitting it in public is the rarer skill.
Example one: understanding is not excusing
Take Adolf Hitler. We read his biography and conclude: monster, madman, end of discussion. A critical thinker accepts the moral verdict but doesn’t stop there. He asks why millions of people followed this man. What part did the hyperinflation of 1923 and the Great Depression play? How did the Nazi party win more than 37% of the vote in July 1932? What made ordinary civil servants organize mass murder?
Plenty of people are offended by questions like these, because surely it is all obvious. Yet these are exactly the questions that explain how it happened and help us recognize similar mechanisms today. Hannah Arendt, reporting on the 1961 trial of Adolf Eichmann, coined the phrase “the banality of evil”. What disturbed her most was that one of the organizers of the Holocaust looked like an average bureaucrat, not a demon.
In their book, Haidt and Greg Lukianoff name the belief that life is a battle between good people and evil people as one of three “Great Untruths” that wreck our thinking. Once we split the world into us and them, we stop asking why, and from there it is a short step to repeating other people’s mistakes.
Example two: the angry customer
Now something less historical and more everyday. A customer walks into a small business and lays into the owner. Call him Mike. Mike’s instinct is to give as good as he gets, with interest, because Mike has never heard of critical thinking.
But Mike runs the business with his wife, Anna, and Anna has somehow picked up the habit. She doesn’t take the attack personally. Instead she asks herself a few questions:
- Why is this customer behaving like this? What actually happened?
- Is he even a little bit right?
- What does he want, talking to us this way?
- What can I do so this ends well for both of us?
It turns out the product really was faulty, and the customer had tried to call three times without getting through. Anna apologizes, explains what went wrong and offers compensation that is actually worth something. The customer leaves calm, and a week later he recommends the business to his friends.
Anna did nothing magical. She separated emotions from facts, checked what was true and made her decision on that basis. Well done, Anna.
How to practice critical thinking every day
You don’t need a course or a diploma for this. A few questions and a little patience will do. Here is the set I try to use myself:
- How do I know this? From a study, an expert, a headline or my brother-in-law at the barbecue?
- Who is saying it, and what’s in it for them? Everybody has an interest. That doesn’t make them liars, but it is worth remembering.
- What is the evidence? One story is an anecdote, not a statistic.
- What else could explain it? Before you decide your neighbor stole your newspaper, check whether the wind took it.
- What would make me change my mind? If the answer is “nothing”, you have a creed, not a view.
- Can I state the other side’s best argument? If not, I probably don’t understand it yet.
- How angry does this make me? The stronger the emotion, the more likely it is that someone is playing your System 1.
In practice it looks like this:
| Reflex | Critical question |
|---|---|
| “Everyone’s talking about it, so it must be true” | Is popularity evidence? |
| “That politician is a liar, so he’s wrong” | Am I judging the argument or the person? |
| “It worked for me, so it works” | How many people did it not help, and has anyone checked? |
| “Cases are rising!” | Relative to what? How many tests were done? |
We all got a crash course in that last question during the pandemic. The same questions are just as useful in the voting booth. And more data will not do the thinking for you: information is not understanding, a point I also make about business in You killed market research.
Why doesn’t school teach critical thinking?
Haidt had a point, though the picture is not hopeless. Researchers have spent decades testing whether critical thinking can be taught, and a 2015 meta-analysis by Philip Abrami and colleagues, pooling 341 effect sizes from experimental studies, found that it can. The average effect was small. Teaching did best when it combined real problems, discussion and mentoring.
The catch is that the skill transfers poorly. As the cognitive scientist Daniel Willingham argued in American Educator in 2007, thinking is not a general skill like riding a bicycle: how well you think about something depends on how much you know about it. A brilliant reader of novels won’t necessarily bring the same care to a supplement ad or a politician’s promises. So a lecture on cognitive biases achieves little. You have to practice on concrete material, one field at a time.
The international numbers are sobering. In PISA 2018, the OECD’s test of 15-year-olds, only 9% of students across OECD countries read well enough to tell fact from opinion when the cues were implicit, up from 7% in 2000. Only 54% said school had taught them to recognize biased information, and countries where more students got that training did better at telling fact from opinion, even after accounting for national wealth. So it can be taught. Schools just reach about half the class.
There is also a less comfortable reason. A student who thinks critically asks awkward questions of teachers, principals, parents and whoever wrote the curriculum. Not every school system wants that, and not every parent does either.
What has changed since 2019?
When I wrote the first version of this post, critical thinking struck me as a useful skill. Today I think it is a survival skill.
- The pandemic showed how quickly misinformation spreads online and how readily people on every side pick only the numbers that suit them.
- Fakes got cheap. Generative AI went mainstream at the end of 2022, and a convincing article, photo or cloned voice now takes seconds to make. “I saw it with my own eyes” has stopped being an argument.
- Platforms stepped back. In January 2025 Meta announced that it would end third-party fact-checking in the United States and switch to Community Notes written by users. Whatever you thought of the old system, more of the checking is now your job.
- Daniel Kahneman died in March 2024. Thinking, Fast and Slow is still the best book to start with. It is also on my list of motivational books worth reading, which tells you what kind of motivation I believe in.
My take
Critical thinking is a habit anyone can build, philosophy degree optional. It starts with one question: “How do I know that?” Then come the others: who is saying it, what evidence they have, and what the best case for the other side looks like.
You won’t always feel like it. System 1 is more comfortable, and outrage is more fun than analysis. But a person who never checks his beliefs doesn’t really hold opinions; he rents them from whoever spoke to him last. If Anna can do it, so can you.
When did you last change your mind about something that mattered?
Questions people ask
What is critical thinking in simple terms?
It is the habit of checking how you know what you know: separating facts from opinions and looking for evidence and other explanations before you reach a conclusion or make a decision.
Can critical thinking be taught?
Yes, though less easily than people assume. A 2015 meta-analysis found that teaching works best with real problems, discussion and mentoring, but the skill transfers poorly from one subject to another.
Why don’t schools teach critical thinking?
Many try, but it is hard to teach as a general skill, because good thinking depends on knowing the subject. In PISA 2018 only 54% of 15-year-olds across the OECD said school had taught them how to spot biased information.
What questions help you think critically?
Start with three: How do I know this? Who is saying it, and what do they gain? What would change my mind? If the answer to the last one is ‘nothing’, you have a creed, not a view.