IQ and rationality: totally uncorrelated?

People can be very smart and have wildly irrational beliefs. Many people find this counter-intuitive, but there are examples that seem too clear-cut to dispute: Sir Isaac Newton was clearly very smart, but was also into alchemy and numerology, and may have even seen his work on those topics as more important than the scientific work remember him for. Kary Mullis won the Nobel Prize for inventing PCR (the technology that makes crime-scene DNA analysis possible), but has promoted HIV denialism and climate change denialism.

For those who find this surprising, Michael Shermer’s classic essay Why Smart People Believe Weird Things attempts to provide some answers:

For those of us in the business of debunking bunk and explaining the unexplained, this is what I call the Hard Question: why do smart people believe weird things? My Easy Answer will seem somewhat paradoxical at first: Smart people believe weird things because they are skilled at defending beliefs they arrived at for non-smart reasons…

For the most part intelligence is orthogonal to and independent of belief. In geometry, orthogonal means “at right angles to something else”; in psychology orthogonal means “statistically independent. Of an experimental design: such that the variates under investigation can be treated as statistically independent,” for example, “the concept that creativity and intelligence are relatively orthogonal (i.e., unrelated statistically) at high levels of intelligence.”

Unfortunately, while Shermer’s essay makes a strong case that intelligence and rationality aren’t the same thing, he doesn’t have much in the way of clear-cut evidence that they’re truly orthogonal as he says. Even if there are very smart, very irrational people in the world, there could still be some correlation between intelligence and rationality.

More recently, though, I ran into some surprising evidence that intelligence and rationality may be truly uncorrelated. In What Intelligence Tests Miss: The Psychology of Rational Thought, Keith Stanovich gives a nice overview of empirical research on the subject. He reports that many studies do find correlations–albeit only modest ones–between intelligence and rationality. However:

If anything, the studies I have reviewed overestimate the linkage between intelligence and rational thinking. This is because many of these studies have given the subjects helpful instructions–for example, they are to put aside their prior opinion and reason in an unbiased manner. There is a pattern in the literature indicating that when subjects are not given such instructions–when they are left free to reason in a biased or unbiased manner according to their wish (as we do in real life)–then the correlations between unbiased reasoning and intelligence are nearly zero.

Later in the book he puts it a little differently:

The point is that, increasingly, cognitive science is coming to a shocking conclusion–a conclusion so important in its ramifications that it deserves to be set apart:

Intelligent people perform better only when you tell them what to do!

I am referring here specifically to the domain of rational thought and action. If you tell intelligent people what a rational requirement is–if you inform them about a particular stricture of rational thought (avoid intransitivity, avoid framing, do not be overconfident in your own knowledge, etc.)–and then give them a task that requires following the stricture, higher-IQ individuals will adhere to the stricture better than individuals of lower intelligence. However, if you give people tasks without warning them that a particular rational principle is involved–if they have to notice themselves that an issue of rationality is involved–individuals of higher intelligence do little better than their counterparts of lower intelligence.

Stanovich also has insightful comments on issues with the folk concept of intelligence. He argues that, in effect, the folk concept of intelligence equivocates between “IQ” and “IQ plus rationality.” This is what explains the seeming paradox of “smart but acting dumb.” Some more quotes:

It is not just that people are confused about what IQ tests assess and what they do not assess. People are also very confused about the concept of intelligence itself. The so-called folk language (everyday usage) of the term intelligence is an utterly inconsistent mess.


I think that folk psychology does now differentiate between rationality and intelligence somewhat, but that folk psychology could be reformed to do this even more.

On this view, it’s fair to say that IQ tests fail to capture everything people mean by “intelligence,” but this is more a problem with the folk concept of intelligence than with IQ tests.

(Personally, I feel like I have a clear understanding of the difference between intelligence and rationality, and mostly feel OK saying that when I talk about “intelligence,” I basically mean IQ. But I’m still tempted to use phrases like “smart people saying stupid things.”)

Edit: One question that remains is if IQ and rationality are unrelated, why do many kinds of irrational beliefs seem uncommon among scientists, and even less common among top scientists? A cynical explanation would be that this is purely the result of the beliefs in question being “out group” in the scientific community. My preferred explanation though, is this reflects training in and a culture of good epistemic habits.


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