Bob is in a bar, looking at Susan. But she is looking at Pablo. Bob is married. Pablo is not.
Is a married person looking at an unmarried person? The answer could be (a) yes, (b) no or (c) cannot be determined.
Give this problem a shot before you keep reading, but don't feel badly if you get it wrong.
Roughly 80 per cent of people choose (c), but it is not the correct answer, says Keith Stanovich, a professor of human development and applied psychology at the University of Toronto.
He studies why smart people do stupid things - or, in more scientific terms, how intelligence is distinct from rationality. His work offers insight into important cognitive abilities that are not measured by IQ tests. It also suggests that deficits in real-world reasoning can be corrected, whether in adults or in children.
He says most people get the Bob-Susan-Pablo problem wrong because they tend to be "cognitive misers" - they put as little mental effort as possible into solving a problem. In this case, they quickly jump to the conclusion that they don't have enough information rather than making the effort to see if they do.
If Susan is married, then a married person is looking at an unmarried person (Pablo) . If she is single, then Bob, a married guy, is looking at an unwed woman. Either way, the answer to the question is yes: A married person is looking at an unmarried one.
Got it wrong? Chalk it up to "dysrationalia," a term Dr. Stanovich has coined for the inability to think and behave rationally despite adequate intelligence, as he details in his recent book, What Intelligence Tests Miss: The Psychology of Rational Thought.
There is, of course, an upside to being a cognitive miser - it means using the brain in an energy-efficient manner. It helps to explain why most of us get out of the house in the morning: We don't waste hours considering what colour socks to wear or what to have for breakfast.
But it also means that when faced with a more complicated decision or question, we tend to give the first response that comes to mind, rather than considering carefully. Most of us are also heavily influenced by how a question is framed.
It is useful to get a handle on dysrationalia, Dr. Stanovich says, because we face many difficult problems that require accurate rational responses, from evaluating environmental threats to deciding how to invest retirement savings.
A rationalist's tool box
However, we can also train ourselves ways to overcome our miserly tendencies. Studies have shown that people can teach themselves a number of techniques to help them consider all the possibilities when deciding among options:
Look, don't leap: Dr. Stanovich and other experts in rational thinking suggest trying not to say the first thing that pops into your head - avoiding what psychologists call "impulsively associative thinking."
Think of the opposite: "Several studies have shown that practice at the simple strategy of triggering the thought 'think of the opposite' can help prevent a host of thinking errors," Dr. Stanovich says.
In the case of the Bob-Susan-Pablo conundrum, to "think of the opposite" would mean reacting against your instincts by supposing that, in fact, you do have enough information to answer yes or no.
Check your emotions: The Bob-Susan-Pablo problem isn't an emotional one, unless you had a romantic entanglement that ended badly with a Bob, Susan or Pablo. But other problems can evoke powerful feelings, such as fear of death, that can influence decisions about whether to have a cancer screening test or what kind of life insurance to buy.
Of course, intuitive or instinctive decision-making can be good in some situations, such as figuring out whether to marry someone or to date them. There is an evolutionary reason so many of us rely on "gut feeling" decisions - they probably served our ancestors well enough for thousands of years.
But emotions can also lead us astray on complex decisions, such as deciding whether to have our children vaccinated or whether to fly in the weeks following a major airline disaster.
The most rational thinkers, it seems, are able to check out their gut feeling, but then think it through in a more analytical fashion.
What don't you know? Reflective deliberation also depends on certain kinds of knowledge. Dysrationalia, Dr. Stanovich says, is also a content problem: What we don't know - about statistics, the principles of probability and rules of scientific thinking - can hinder our ability to come to rational decisions.
Understanding the role of a control group in a medical experiment, for example, is essential for evaluating whether a drug is effective.
Start in school
These kinds of concepts are teachable, Dr. Stanovich says - certainly in high school, if not earlier. Children may not understand control groups, but they can comprehend simple rules for scientific thinking, such as, "Would the same thing have happened if you hadn't done anything?"
So far, however, Dr. Stanovich says there are only a smattering of such critical-thinking programs in schools anywhere, and many of those are not systematically grounded in cognitive science.
In theory, both adults and kids can train their brains to be more rational and less miserly. It could lead to better decision-making - not to mention the satisfaction of coming up with the correct answers to brain teasers that demonstrate how instinctive reasoning can lead us astray.
Try this one, written by Hector Levesque, an expert in artificial intelligence at the University of Toronto:
There are three toy blocks stacked up. The top one is green and the bottom one is red. Is there a green block directly on top of a non-green one? The answer could be (a) yes, (b) no or (c) cannot be determined.
Think of all of the possibilities. Think of the opposite of your initial answer. The correct answer is (a) yes.
Anne McIlroy is The Globe and Mail's science reporter, specializing in learning and the brain.
Tease your reason
Are you a cognitive miser? Try these problems.
1. A toy puck and a hockey stick cost $1.10 in total. The stick costs $1 more than the puck. How much does the puck cost?
2. If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?
3. In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of it?
1. Five cents.
2. Five minutes.
3. 47 days
Source: Shane Frederick, now at the Yale School of Management, in an article published in the Journal of Economic Perspectives (2005).