Why Intelligent People Do Foolish ThingsSociety is replete with examples of intelligent people doing foolish things. This seems puzzling considering that intelligent people (as indicated by intelligence tests and their proxies — SAT scores, etc.) are generally thought of as rational, smart people.

So it may come as a surprise to find out that intelligent people are not necessarily rational people. Or, it may surprise some people to learn there is more to good thinking than intelligence. In fact, intelligence is a weak to moderate predictor of many rational thinking skills.

And in some instances, intelligence shows zero correlation with rational thinking skills.

An example of the dissociation of intelligence and rationality is seen with myside bias. Myside bias is displayed when people evaluate and gather evidence in a manner biased toward their own beliefs and opinions.

In a series of experiments Stanovich and West (2008) examined the association between cognitive ability and two cardinal critical thinking skills- avoidance of myside bias and avoidance of one-side bias. (One-side bias is demonstrated when people prefer one-sided arguments over arguments presenting multiple perspectives.)

In Experiment 1 natural myside bias was investigated in 15 different propositions. In Experiment 2 myside bias and one-side bias was studied. In Experiment 3 associations between thinking dispositions — in addition to cognitive ability — and one-side and myside bias were investigated.

In Experiment 1, the researchers concluded, there was “no evidence at a ll that myside bias effects are smaller for students of higher cognitive ability” (p. 140). The main purpose of Experiment 2 was to investigate the association of cognitive abilities with myside and one-side bias. “The results… were quite clear cut. SAT total scores displayed a nonsignificant 7.03 correlation with the degree of myside bias and a correlation of .09 with the degree of one-side bias (onebias1), which just missed significance on a twotailed test but in any case was in the unexpected direction” (p. 147).

It was also revealed that stronger beliefs usually imply heavier myside bias.

In Experiment 3 “the degree of myside bias was uncorrelated with SAT scores,” and “[t]he degree of one-side bias was uncorrelated with SAT scores” (p. 156). Myside bias was weakly correlated with thinking dispositions. One-side bias showed no correlation with thinking dispositions.

When discussing research on intelligence, we are referring to narrow theories of intelligence — those mental abilities measured by the tests mentioned above. These theories provide a scientific concept of intelligence generally symbolized as g, or “in some cases where the fluid / crystallized theory is adopted intelligence (Gf) and crystallized intelligence (Gc)” (Stanovich, 2009, p. 13).

Fluid intelligence reflects reasoning abilities (and, to a degree, processing speed) across a variety of domains, particularly novel ones. Crystallized intelligence reflects declarative knowledge acquired by acculturated learning — general knowledge, vocabulary, and verbal comprehension, etc. Mental abilities assessed by intelligence tests are important, but the assessment of a variety of important mental abilities is missed by intelligence tests.

Cognitive scientists generally identify two types of rationality: instrumental and epistemic. Instrumental rationality can be defined as adopting appropriate goals, and behaving in a manner that optimizes one’s ability to achieve goals. Epistemic rationality can be defined as holding beliefs that are in line with available evidence. This type of rationality is concerned with how well our beliefs map into the structure of the world. In order to optimize rationality one needs adequate knowledge in the domains of logic, scientific thinking, probabilistic thinking, and causal reasoning. A wide variety of cognitive skills fall within these broad domains of knowledge. Many of these skills are not assessed on IQ tests.

Keith Stanovich coined the word dysrationalia, “meaning the inability to think and behave rationally despite having adequate intelligence” (Scientific American Mind, 2009, p. 34; “What Intelligence Tests Miss,” 2009, p. 18). Rationality encompasses good judgment and decision-making, and it is just as important as intelligence.

Why do we act and behave irrationally? Two broad categories contribute to this problem: a processing problem and a content problem. When choosing the cognitive strategies to apply when solving a problem we generally choose the fast, computationally inexpensive strategy. Although we have cognitive strategies that have great power, they are more computationally expensive, are slower, and require more concentration than the faster, cognitively thrifty strategies. Humans naturally default to the processing mechanisms that require less effort, even if they are less accurate. Individuals with high IQs are no less likely to be cognitive misers than those with lower IQs.

A second source of irrational thinking — content problem — can occur when we lack specific knowledge to think and behave rationally. David Perkins, Harvard cognitive scientist, refers to “mindware” as rules, strategies, and other cognitive tools that must be retrieved from memory to think rationally (Perkins, 1995; Stanovich, 2009). The absence of knowledge in areas important to rational thought creates a mindware gap. These important areas are not adequately assessed by typical intelligence tests. Mindware necessary for rational thinking is often missing from the formal education curriculum. It is not unusual for individuals to graduate from college with minimal knowledge in areas that are crucial for the development of rational thinking.

There have been a variety of tests developed to assess rational thinking skills. Utilizing tests of rationality are just as important as tests of intelligence. Rational thinking skills are learnable, and with the development of rational thinking skills we can expect better judgment and decision making in everyday life. Because of irrational thinking “physicians choose less effective medical treatments; people fail to accurately assess risks in their environment; information is misused in legal proceedings;” (Stanovich, 2009), millions of dollars are spent on government and private industry; millions and millions of dollars are spent on dietary supplements and so on.

Stanovich and colleagues recently introduced a taxonomy or irrational thinking tendencies and their relation to intelligence. As mentioned earlier, intelligence has shown a weak to moderate correlation with some rational thinking skills while nearly zero with others. Good thinking is more than intelligence; it is rationality. Intelligence tests do not adequately assess rational thinking skills.

How does one improve rational thinking skills? In a recent interview I asked the Stanovich research lab to address this question (Hale, 2010). They answered with the following: “[a] good first start is education, which readers have already started here by reading this blog entry. Having an understanding of how cognitive scientists have expanded what is meant by rationality is important, namely that rationality is about two critical things: What is true and what to do.”


Hale, J. (2010). Dysrationalia: Intelligent People Behaving Irrationally. Knowledge Summit. [accessed November 16, 2010]

Perkins, D. (1995). Outsmarting IQ: The emerging science of learnable intelligence. New York: Free Press.

Stanovich, K. (2009). What Intelligence Tests Miss: The Psychology of Rational Thought. New Haven, Connecticut: Yale University Press.

Stanovich, K. (2009). Rational and Irrational Thought: The Thinking that IQ Tests Miss. Scientific American Mind. Nov/ Dec [accessed October 4, 2010]

Stanovich, K , & West, R. (2008). On the failure of cognitive ability to predict myside and one-sided thinking biases. Thinking and Reasoning. 2008, 14 (2), 129 – 167.