The way of thinking that asks what is being claimed, on what grounds and what would change your mind. It works by breaking reasoning into its parts and holding each one to a standard.
Take the claim apart and ask what would have to be true
Critical thinking, in Ennis’s definition, is reasonable reflective thinking focused on deciding what to believe or do. Its tools take an argument apart: the claim, the evidence, the assumptions, the inferences that connect them. Paul and Elder list eight elements of reasoning and a set of standards to hold each against. It is strongest when a decision rests on a claim that could be wrong. It is weakest when there is no claim to test yet, and it depends heavily on knowing the subject.
In ordinary life
A headline says that people who drink coffee live longer. A critical thinker asks what was actually measured, in whom, compared with what and what else coffee drinkers might have in common. Most of the time the study is more careful than the headline, and says less.
Kahneman describes a mind that jumps to a coherent story from whatever evidence is in front of it. He calls it "what you see is all there is". Critical thinking is the slower habit of asking what you are not seeing, and whether the story would survive it.
The skill is weighing. Doubting everything equally is as lazy as believing everything. Some claims deserve more scrutiny than others, and the useful question is always what evidence would change your mind. Willingham’s caution applies here. You can only weigh evidence in a field you know. Critical thinking about coffee needs some idea of how nutrition studies work.
The educational experience
Every page follows the same Singapore secondary school on the same kind of day. The school wants to give Secondary 1 one afternoon a week for a project that crosses Geography, Science and English Language, and the proposal is due for a decision. The five people and the situation stay fixed. Only the way of thinking changes.
All five, interconnected
The five threads as they were written, interleaved, so the hand-offs between them are visible. Pick a person to follow their day on its own. The people are illustrative, and the same five appear on every way’s page.
07:30
Mdm Kavitha, between deliveries
She forwards an article to the family chat: schools that swap lessons for projects see results fall. She adds three worried faces. Arjun’s cousin replies with a different article saying project learning raises results.
09:00
Mr Hafiz, preparing the decision
Two claims sit on his desk. The proposal cites a study in which project-based learning raised attainment by a wide margin. The HOD Science says losing a period a week will cost Secondary 1 a grade in the end-of-year exams. He asks Ms Chen to check both, her own included.
10:45
Ms Chen, free period
She has no statistics, so she uses Paul and Elder’s elements instead: what was measured, in whom, against what. Her study compared schools that volunteered for projects with schools that did not, and measured project grades and engagement. The claim is that students learn more. What was shown is that volunteering schools liked their projects.
11:30
Arjun’s Geography class
Ms Chen gives the class the two articles from the family chat, without saying where they came from. In pairs they list what each one measured. Arjun, who rarely speaks, writes on the sheet that one study tested students on their projects and the other tested them on the old exams.
11:50
Arjun, same lesson
With his nod, Ms Chen reads his note aloud. The class argues about which test the school should care about. Nobody wins, which Ms Chen counts as a success. Arjun does not join the argument, but he keeps writing.
13:00
Ms Chen and Mr Hafiz
She shows him the gap in her own study, then turns to the Science claim. The lost grade is an estimate from the scheme of work, not a measure. Nobody has tested what Secondary 1 students forget when a period goes. Mr Hafiz asks what evidence would convince each side, and writes both answers down.
15:00
Dr Ong, drafting her advice
She has nine reports on her desk, five for project-based learning and four against. She stops counting them and sorts them by what they measured. They sort into tested on projects and tested on subject exams, and barely disagree once sorted. The syllabuses she advises on are written entirely in the second kind.
16:30
A call between Dr Ong and Mr Hafiz
They agree a term’s pilot could work on one condition. Secondary 1 sit the usual weighted assessments, and the project work is assessed separately, so the school can see both. Neither of them is sure who will do the second round of marking.
19:45
Arjun and Mdm Kavitha, packing the evening orders
Arjun explains the two studies while Mdm Kavitha seals the containers. She asks which one is right. He says that is the wrong question, and then has to explain why, which takes until the delivery rider is at the door.
The evidence stayed the same all day. The question asked of it changed. Sorting the claims by what they measured dissolved most of the disagreement and left a real one: which kind of learning the school wants to count, and who will do the counting. Critical thinking found that question but could not answer it, and the decision is still due.
Implications
The same five dimensions for all four ways. This is the part that can be tabulated. The two narratives above are the part that can be argued with.
The gap between what is claimed and what was shown. Critical thinking notices when a measure has been swapped for the thing it stands in for, when an assumption is carrying the argument and when two sources that seem to disagree are answering different questions.
Anything that has not yet been claimed. Critical thinking needs something to evaluate, so it is weak at the start of a problem and at generating options. It can also make a group very good at finding flaws in every proposal and very slow at making one.
It sees arguments more clearly than it sees structures. A set of individually sound decisions can still add up to a bad pattern, and no amount of scrutinising each decision will reveal it.
Knowledge first. Willingham’s argument is that critical thinking cannot be taught as a general skill cut loose from content, because what counts as good evidence differs between history and chemistry. Teachers need to teach it inside their subject. Students need to be allowed to reach conclusions, not only to find faults.
Good work names what evidence would change the writer’s mind. Weak work lists objections to every side and settles on none.
Behind the question of what to measure. In the day above, critical thinking cleared away the false disagreement and then stopped at the real one: whether the school cares more about what students can show in a project or in a subject test. That is a question about purpose. The Delphi Report’s experts included fair-mindedness among the dispositions of a critical thinker, which is an admission that the method needs values it cannot supply.
The hollow version is a poster of question stems and a generalised scepticism that treats every claim as equally doubtful. It teaches students to say "but what about bias?" about everything. That is a verbal habit, and it can make a class more confident and less accurate at the same time.
Reading
Published works only. Start with the first on the list.
Ennis, R. H. (1996). Critical Thinking. Prentice Hall.
Critical thinking as reasonable reflective thinking focused on deciding what to believe or do.
Paul, R., & Elder, L. (2006). The Miniature Guide to Critical Thinking: Concepts and Tools. Foundation for Critical Thinking.
The eight elements of reasoning and the intellectual standards to hold them to.
Facione, P. A. (1990). Critical Thinking: A Statement of Expert Consensus for Purposes of Educational Assessment and Instruction (The Delphi Report). American Philosophical Association.
An expert consensus on the skills and dispositions involved.
Willingham, D. T. (2007). Critical thinking: Why is it so hard to teach? American Educator, 31(2), 8–19.
Why critical thinking does not transfer well without knowledge of the domain.
Kahneman, D. (2011). Thinking, Fast and Slow. Farrar, Straus and Giroux.
Why the mind builds a coherent story from whatever is in front of it.