On Teaching Critical Thinking

As someone who was teaching critical thinking for a living well before anyone thought to call it a '21st century skill' it bothers me to no end to read articles like this arguing that we should not be teaching critical thinking in schools.

It feels to me that the critics of critical thinking do not understand what critical thinking is, nor why we would teach it. Thus Carl Hendrick describes the critical thinking as follows:
the aim is to equip students with a set of general problem-solving approaches that can be applied to any given domain; these are lauded by business leaders as an essential set of dispositions for the 21st century. 
Well.... no. That's not what critical thinking is. Critical thinking is neither "a set of general problem-solving approaches" nor is it a "disposition". Critical thinking does apply to any given domain, for reasons I'll explain below. And it's irrelevant whether they are lauded by business leaders.

The most common argument against critical thinking (favoured also by Daniel Willingham) is this:
to be good in a specific domain you need to know a lot about it: It's not easy to translate those skills to other areas.
This non-translatability of cognitive skill is well-established in psychological research and has been replicated many times.
Moreover, they argue that critical thinking does not contribute to improved learning outcomes. Citing a study of 'brain training' games, Hendrick quotes:
We know of no evidence for broad-based improvement in cognition, academic achievement, professional performance, and/or social competencies that derives from decontextualized practice of cognitive skills devoid of domain-specific content.
Fair enough. Let's take all this as a given.

Critical thinking, however, is not the translation of specialized skills from one domain to another. Nor is it even intended to support the learning of a specialized domain - you need a lot of practice and hands-on experience to do that. Nor are the 'brain training' games an example of critical thinking.

So what is critical thinking good for? Hendricks almost had it when he said this:
we all know people who are "clever" in their professional lives yet who often seem to make stupid decisions in their personal lives.
Yes! Exactly! Critical thinking is designed to prevent this!

So how can critical thinking accomplish anything useful? After all, it is true that you do need to know things in order to reason critically about them. Happily, first, we almost never have no knowledge of a subject. And second, critical thinking is one of those things we need to know.

Let me offer an analogy: mathematics. This is a type of very general knowledge that is applied in a wide range of domains. There are some useful things to note about mathematics:
  • it applies everywhere, regardless of context. There are no domains in which 2+2 does not equal 4. 

  • nobody pretends that it is the whole of any other discipline. Of course you have to have some knowledge about physics to use mathematics in physics. And the knowledge of physics doesn't transfer to other domains (but the mathematics does).

  • knowledge of mathematics will help you a lot in everyday life, and help you spot (or prevent) glaring errors of reasoning even in domains you know little about. 
For example, I know nothing about aviation. But I can demonstrate that 100 kilograms of fuel is different from 100 pounds of fuel, which tells me that if the pilot uses 'kilograms' and the ground crew uses 'pounds', someone is in for a rude surprise. Or if the range of the aircraft is 1600 kilometers, and the flight plan is 1605 kilometers, there's a risk the flight might end tragically.

This might seem pretty basic. But so are the principles of reasoning that characterize critical thinking (and as someone who taught it, watching people get it wrong feels the same as watching someone say 2+2=5 ... and getting away with it).

So if critical thinking isn't a problem-solving set of dispositions (nor empty advice to 'consider all perspectives' and other de Bono truisms) then what is it?

In the first place, critical thinking is the application of the basic principles of logic, usually beginning with the propositional calculus and categorical syllogisms (if you took my course you'd know what those terms mean). Here's an example of each:

Propositional calculus:

If A then B
Therefore B

Categorical syllogism

All A are B
All B are C
Therefore, All A are C

The point of both of these principles is that you can replace A, B and C with anything, and it still works. It doesn't matter what domain you are working in. Just as 2+2 always yields 4, If A then B, and A always yields B. There are many more such principles, and indeed whole other branches of logic that form the basic of our comprehension of any domain: inductive reasoning, quantification, modalities, probabilities, and more.

Now there is a skill involved in applying these. There are, for example, many ways to say "If A then B". A lot of the time, in practical life, people skip that statement entirely, and it has to be assumed. Being able to read text, and identify these patterns, is an essential skill (even more essential than the 'word problems' that are their counterpart in mathematics). And these skills apply independently of the domains.  The words may vary, but the principles remain the same.

This leads us to consider a second example of a generic skill that applies in a wide range of domains. Mathematics was the first. And the second? Grammar.

In all disciplines, a sentence needs to have a subject and a predicate in order to have a fixed or specific meaning. Pronouns need to agree with nouns, or at least be employed in a context where some sort of agreement can be assumed. The role of propositions is the same in geography as it is in avionics, and they appear in the same places in sentences.

Grammar, and language generally, are not a part of physics (or of any specialized discipline), but physics cannot operate without them.

There is a close relationship between critical thinking and grammar. The formal "If A then B, A, therefore B" maps to the linguistic structure of a language, and we express the condition in the subjunctive sense ("if wishes were horses...). Knowing how to form a sentence is part and parcel of knowing how to reason. For this reason, a great deal of critical thinking revolves around reading comprehension.

Another, broader, part of critical thinking involves the comprehension and criticism of larger cognitive structures. here are generally thought to be four major types of structures (and favious lesser structures, such as interrogation):
  • Argumentation - the offering of reasons that lead to a conclusion
  • Explanation - the identification of causes or reasons that something is the case (and ultimately the basis for the scientific method)0
  • Definition - the fixing of meanings of terms through reference, representation, ostension or other means
  • Description - the presentation of events and states of affairs, including attributions of properties, categorizations, relations, and connections
Each of these operates in any given discipline (indeed, the absence of any of these four major types of structures in a discipline is prima facie evidence that it is a pseudo-discipline).

Most critical thinking courses focus on argumentation, since the giving of reasons to believe a conclusion is fundamental to pretty much any discipline (argumentation, for example, is always offered in response to a question like 'what should I do?'). And the principles for evaluating arguments do not vary from discipline to discipline.

That's not to say that every discipline is the same as every other. There are key differences between disciplines. Some of the major differences include:
  • what makes a question worth asking (and what questions are really worth asking).
  • what facts are relevant to the resolution of problems and states of affairs
  • what counts as evidence, and what makes a statement true or false
These are pretty big differences. Cavernous. These are what make the arguments offered by Hendricks and Willingham seem so intuitive. Any time you need to know whether or not something is true, you've gone outside the bounds of critical thinking, and entered into one or another specific discipline.

And that takes us to the third major area of critical thinking: identifying errors or fallacies of reasoning. And as you may suspect, you don't need to be an expert in a discipline to be able to tell that an error of reasoning has been committed. These have been drawn up in various guides, including one of my own, to the logical fallacies.

And here's the kicker: there are no disciplines in which any of these fallacies count as good reasoning. The whole point of a fallacy is that it is not an error of fact or of evidence (again, these are the things that are domain-specific). A fallacy is a common form of error (just like failing to carry is a common error in mathematics).

It takes skill to identify and correct logical fallacies. If you have domain knowledge you will be better at it in a specific domain, but even if you have no domain knowledge, you can avoid the consequences of some of the more egregious errors. Invalid syllogisms, misrepresentation of information, distortion of data - all these are errors in all disciplines, and can be spotted by amateurs and experts alike.

The teaching of critical thinking equips students with essential core skills that are needed in any discipline, based on principles that are as fundamental as  mathematics and language (indeed, for the purists, you can read an argument shoring that they are all in fact the same things).

Like the teaching of any discipline, it requires not so much the presentation of facts and principles as it does the application of these principles in varied and authentic environments. And like mathematics, the teaching of critical thinking can be adapted to a student's existing knowledge, developing skills and abilities that will be useful - and transferable - to much more complex disciplines in later life.


  1. Let me first complement your generosity of spirit for taking the trouble to respond to the risible essay posted in the AERA group on LnkedIN, ostensibly about "teaching critical thinking" that simply erected an unrecognizable and non-sensical "straw man" definition of "critical thinking" only to smack it down with illogic, false equivalences and bogus analogies. I was not surprised to see only 2 or 3 (of 23) posts point out some of the flaws in the piece (not sure "flaw" is sufficient as an adjective for not knowing what critical thinking actually is...)

    My first thoughts as I read the piece jumped to a notion I once read that perhaps you can place for me: something to the effect that "critical thinking requires having sufficient knowledge in some domain _about which one can think critically_". Which sounds to me a bit like something Roger Benjamin would say -- the CAE's "collegiate learning exam" (now CLA+ etc) has focused more or less on CT over the last decade or so if it's life. And CAE shows some some rigor in thinking about the "measurement" aspects of CT and assessment -- more so than the "big players" in standardized testing, at least. But alas, I have not yet found the source. Perhaps that might have set Mr. Hendrick off in a more constructive direction...

    I will write you separately, but keep up the good work. Not the first time something you've said online on the subjects of online learning, cognition, etc. has brought me to your site. will sign up for your newsletter.


  2. There is a range of argumentation based on the need for 'content knowledge' over skills, method, activity, or process. A cluster of what I generally call 'instructivists' push this line (and I say 'push' because it manifests more as a political movement than as a line of research). The names I mainly associate with it are people like Paul Kirschner and Daniel Willingham.


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