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Daniel Dennett’s Most Useful Critical Thinking Tools

We recently discussed some wonderful mental tools from the great Richard Feynman. Let's get some more good ones from another giant, Daniel Dennett.

Dennett is one of the great thinkers in the world; he's been at the forefront of cognitive science and evolutionary science for over 50 years, trying to figure out how the mind works and why we believe the things we believe. He's written a number of amazing books on evolution, religion, consciousness, and free will. (He's also subject to some extreme criticism due to his atheist bent, as with Dawkins.)

His most recent book is the wise and insightful Intuition Pumps and Other Tools for Critical Thinking, where he lays out a series of short essays (some very short — less than a page) with mental shortcuts, tools, analogies, and metaphors for thinking about a variety of topics, mostly those topics he is best known for.

Some people don't like the disconnected nature of the book, but that's precisely its usefulness: Like what we do here at Farnam Street, Dennett is simply trying to add tools to your toolkit. You are free to, in the words of Bruce Lee, “Absorb what is useful, discard what is useless and add what is specifically your own.”


The book opens with 12 of Dennett's best “tools for critical thinking” — a bag of mental tricks to improve your ability to engage critically and rationally with the world.

Let's go through a few of the best ones. You'll be familiar with some and unfamiliar with others, agree with some and not with others. But if you adopt Bruce Lee's advice, you should come away with something new and useful.

Making mistakes

Mistakes are not just opportunities for learning; they are, in an important sense, the only opportunity for learning or making something truly new. Before there can be learning, there must be learners. There are only two non-miraculous ways for learners to come into existence: they must either evolve or be designed and built by learners that evolved. Biological evolution proceeds by a grand, inexorable process of trial and error–and without the errors the trials wouldn't accomplish anything. As Gore Vidal once said, “It is not enough to succeed. Others must fail.”


The chief trick to making good mistakes is not to hide them–especially not from yourself. Instead of turning away in denial when you make a mistake, you should become a connoisseur of your own mistakes, turning them over in your mind as if they were works of art, which in a way they are. The fundamental reaction to any mistake ought to be this: “Well, I won't do that again!”

Reductio ad absurdum

The crowbar of rational inquiry, the great lever that enforces consistency, is reductio ad absurdum–literally, reduction (of the argument) to absurdity. You take the assertion or conjecture at issue and see if you can pry any contradictions (or just preposterous implications) out of it. If you can, that proposition has to be discarded or sent back to the shop for retooling. We do this all the time without bothering to display the underlying logic: “If that's a bear, then bears have antlers!” or “He won't get here in time for supper unless he can fly like Superman.”

Rapoport's Rules

Just how charitable are you supposed to be when criticizing the views of an opponent? […] The best antidote I know for [the] tendency to caricature one's opponent is a list of rules promulgated by the social psychologist and game theorist Anatol Rapoport (creator of the winning Tit-for-Tat strategy in Robert Axelrod's legendary prisoner's dilemma tournament).

How to compose a successful critical commentary:

1. You should attempt to re-express your target's position so clearly, vividly, and fairly that your target says, “Thanks, I wish I'd thought of putting it that way.”
2. You should list any points of agreement (especially if they are not matters of general or widespread agreement).
3. You should mention anything that you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.

Sturgeon's Law

The science-fiction writer Ted Sturgeon, speaking at the World Science Fiction Convention in Philadelphia in September 1953, said,

When people talk about the mystery novel, they mentioned The Maltese Falcon and The Big Sleep. When they talk about the western, they say there's The Way West and Shane. But when they talk about science fiction, they call it “that Buck Rogers stuff,” and they say “ninety percent of science fiction is crud.” Well, they're right. Ninety percent of science fiction is crud. But then ninety percent of everything is crud, and it's the ten percent that isn't crud that's important, and the ten percent of science fiction that isn't crud is as good as or better than anything being written anywhere.

This advice is often ignored by ideologues intent on destroying the reputation of analytic philosophy, evolutionary psychology, sociology, cultural anthropology, macroeconomics, plastic surgery, improvisational theater, television sitcoms, philosophical theology, massage therapy, you name it. Let's stipulate at the outset that there is a great deal of deplorable, stupid, second-rate stuff out there, of all sorts.

Occam's Razor

Attributed to William of Ockham (or Occam), the fourteenth century logician and philosopher, this thinking tool is actually a much older rule of thumb. A Latin name for it is lex parsimoniae, the law of parsimony. It is usually put into English as the maxim “Do not muliply entities beyond necessary.” The idea is straightforward: Don't concoct a complicated, extravagant theory if you've got a simpler one (containing fewer ingredients, fewer entities) that handles the phenomenon just as well. If exposure to extremely cold air can account for all the symptoms of frostbite, don't postulate unobserved “snow germs” or “arctic microbes.” Kepler's laws explain the orbit of the planets; we have no need to hypothesize pilots guiding the planets from control panels hidden under the surface.

Occam's Broom

The molecular biologist Sidney Brenner recently invented a delicious play on Occam's Razor, introducing the new term Occam's Broom, to describe the process in which inconvenient facts are whisked under the rug by intellectually dishonest champions of one theory or another. This is our first boom crutch, an anti-thinking tool, and you should keep your eyes peeled for it. The practice is particularly insidious when used by propagandists who direct their efforts at the lay public, because like Sherlock Holmes' famous clue about the dog that didn't bark in the night, the absence of a fact that has been swept off the scene by Occam's Broom is unnoticeable except by experts. 


…It is even harder to achieve what Doug Hofstadter calls joosting, which stands for “jumping out of the system.” This is an important tactic not just in science and philosophy, but also in the arts. Creativity, that ardently sought but only rarely found virtue, often is a heretofore unimagined violation of the rules of the system from which it springs. It might be the system of classical harmony in music, the rules for meter and rhyme in sonnets (or limericks, even), or the canons of good taste or good form in some genre of art. Or it might be the assumptions and principles of some theory or research program. Being creative is not just a matter of casting about for something novel–anbody can do that, since novelty can be found in any random juxtaposition of stuff–but of making the novelty jump out of some system, a system that has become somewhat established, for good reasons.

When an artistic tradition reaches the point where literally “anything goes,” those who want to be creative have a problem: there are no fixed rules to rebel against, no complacent expectations to shatter, nothing to subvert, no background against which to create something that is both surprising and yet meaningful. It helps to know the tradition if you want to subvert it. That's why so few dabblers or novices succeed in coming up with anything truly creative.

Rathering (Anti-thinking tool)

Rathering is a way of sliding you swiftly and gently past a false dichotomy. The general form of a rathering is “It is not the case that blahblahblah, as orthodoxy would have you believe; it is rather that suchandsuchandsuch–which is radically different.” Some ratherings are just fine; you really must choose between the two alternatives on offer; in these cases, you are not being offered a false, bur rather a genuine, inescapable dichotomy. But some ratherings are little more than sleight of hand, due to the fact that the word “rather” implies–without argument–that there is an important incompatibility between the claims flanking it.

The “Surely” Operator

When you're reading or skimming argumentative essays, especially by philosophers, here is a quick trick that may save you much time and effort, especially in this age of simple searching by computer: look for “surely” in the document, and check each occurrence. Not always, not even most of the time, but often the world “surely” is as good as a blinking light in locating a weak point in the argument….Why? Because it marks the very edge of what the author is actually sure about and hopes readers will also be sure about. (If the author were really sure all the readers would agree, it wouldn't be worth mentioning.)

The Deepity

A “deepity” is a proposition that seems both important and true–and profound–but that achieves this effect by being ambiguous. On one reading it is manifestly false, but it would be earth-shaking if it were true; on the other reading it is true but trivial. The unwary listener picks up on the glimmer of truth from the second reading, and the devastating importance from the first reading, and thinks, Wow! That's a deepity.

Here is an example. (Better sit down: this is heavy stuff.)

Love is just a word.


Richard Dawkins recently alerted me to a fine deepity by Rowan Williams, the Archbishop of Canterbury, who described his faith as a

silent waiting on the truth, pure sitting and breathing in the presence of a question mark.


Still Interested? Check out Dennett's book for a lot more of these interesting tools for critical thinking, many non-intuitive. I guarantee you'll generate food for thought as you go along. Also, try checking out 11 Rules for Critical Thinking and learn how to be Eager to be Wrong.