Intelligence is required to be able to know that a man knows not.


Although it’s become a truism to say we know relatively little about how our brains work, we know a lot more now than we used to. Naturally, everything we know is contingent and subject to addition, but that doesn’t mean we can ignore it or pretend we don’t know enough to draw some fairly clear conclusions. Despite the many myths surrounding it, intelligence is a good candidate for being the most well researched and best understood characteristic of the human brain. It’s also probably the most stable construct in all psychology. So, what is it?

Intelligence has been described variously, as a capacity for logic, understanding, self-awareness, creativity, problem solving and the ability to learn new information more quickly. According to some it’s the ability to acquire and apply knowledge, while others see it as plain old ‘good sense’. Whatever it is, it seems safe to agree that it’s not simply one thing.

One generally accepted definition is that intelligence is

A very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—”catching on,” “making sense” of things, or “figuring out” what to do.

This being the case, who wouldn’t want to be cleverer? This is a far cry from the oft-repeated truism that all IQ tests show is how good you are at taking IQ tests. In actual fact, IQ has more predictive power than any other psychological construct. I’ve written before about the differences between fluid (Gf) and crystallized intelligence (Gc) and why we should probably concentrate on trying to raise crystallized intelligence and stop worrying about its fluid cousin. Here’s a brief summary of those differences:

An IQ test attempts to measure both Gf and Gc to provide an estimate of an individual’s general cognitive ability.

Before we go any further, we also need to understand that intelligence and IQ are not the same thing – IQ is just a proxy for measuring intelligence. That said, it’s a very robust proxy. Intelligence is measured by a battery of tests designed to assess a range of different mental capabilities. These typically consist of reasoning ability, memory, knowledge (including vocabulary and general knowledge) spatial ability and processing speed.

Here are a few examples of the sorts of questions asked in an IQ test. Matrix reasoning tests are designed to test fluid intelligence because it’s supposed to be possible to work out the answer without any prior knowledge. Here’s a fairly straightforward example:

Select a suitable figure from the four alternatives that would complete the figure matrix:

They can get a lot harder. An example of something that would test crystallised intelligence is a vocabulary test. Clearly, you can only answer the following question with any confidence if you have previously encountered the answer in some other context:

What is the best synonym for dismay?

  1. display
  2. jealousy
  3. provocation
  4. disappointment

A test of verbal reasoning requires you to engage in some reasoning for which you won’t be expected to have any specialised prior knowledge, but the better your vocabulary and general knowledge, the easier you’re likely to find it:

Afro-Eurasia is the largest landmass of all time.

  1. True
  2. False
  3. Cannot say

A properly conducted IQ test takes around 2 hours to sit.

Intuitively, we tend to believe that individuals might have a great memory, but struggle to add up columns of numbers, or possess extensive vocabulary knowledge but struggle to see patterns, or score well on tests of processing while being a bit rubbish at, say, rotating 3D images. It turns out that people who do well at one aspect on an intelligence test, tend to do well at all aspects. In other words, intelligence seems to be general.

In order to understand this counter intuitive finding we have to resist the temptation to think in anecdotes and instead attempt to think statistically. Claims, which may not be true for individuals, may well be the case when we make them about a representative sample of a population. The claims I’ll make about intelligence in this and subsequent chapters are true on average. They are probabilistic. Of course there will always be individuals who defy probability, but that doesn’t mean we’re unable to identify patterns that are the case for the majority. These patterns are correlations. That is, imperfect connections between two variables.

So, while I’m not claiming that a high IQ score causes people to be more creative, or to live longer, there is a correlation which is down to more than chance. This could mean that creativity causes intelligence, or that some other factor – maybe social background – cause both intelligence and creativity. Or it could be some other combination of all three. The point is, the connection is not random. When I say that people who are good at reasoning also have better vocabularies, I’m saying that this isn’t a matter of luck. So while correlation is not proof that one thing causes another, causation is implied. The same is true of the finding that when we look at IQ test results for a reasonably large sample of people, their scores in different areas correlate positively. This what is referred to as the general factor of intelligence. Or the g-factor. Or just g. Nobody knows for sure exactly why this should be the case, but nevertheless, intelligence researchers agree that it is.

Maybe the most surprising finding to come out of intelligence research is that intelligence is a good predictor of longevity; the higher your IQ, the longer you’re likely to live. It’s difficult to understand how the kinds of things measured by IQ tests could correlate with lifespan, but correlate they do. If we’re to understand why it’s so important to make kids cleverer we need to try to get to grips with this baffling discovery.

It seems much more reasonable for longevity to correlate with physical health, and indeed it does, but better health is also positively correlated with higher IQ. This might have something to do with the connection between intelligence and education (more on that later) as the better educated you are, the more likely you are to know how to take care of yourself and to afford to do so, because, you guessed it, intelligence also correlates with success in the workplace.

It’s probably not too much of a shock to find out that higher IQ scores are related to higher income, but more surprising is research that demonstrates the correlation with workplace performance. The more intelligent an employee, the more conscientious they’re likely to be. In fact, the correlations just keep coming as we can see:

There are pretty strong correlations with performing in jobs designated as ‘high complexity’ and ‘medium complexity’ and intelligence even makes a difference when the job is relatively straightforward. IQ even shows correlations with leadership and creativity indicating that, on average, cleverer people will have more ideas and be better at getting others to implement them.

It’s often argued that IQ tests don’t measure important cognitive qualities like creativity, but studies into the links between g and creativity have shown a moderate positive correlation. One problem is that creativity is itself tough to pin down so researchers rely on proxies like ‘divergent thinking,’ but people who do well on IQ tests also do well on the alternative use test “How many uses for a paper clip can you come up with?” (Nusbaum & Silvia 2011) More interestingly, they also do better on tests of musical discrimination (Mosing 2014) and have even been shown to register more patents for new inventions and receive more awards for artistic endeavours. (Wai, J. et al. 2005

If you’re not already convinced of the importance of intelligence, then what about the fact that higher IQ is positively correlated not only with better physical health, but also better mental health. The more intelligent you are, the less likely you will be hospitalised for a psychological condition. Contrary to many popular myths, there’s an especially strong link between higher IQ and lower likelihood of suffering with schizophrenia.

Whilst it seems to be the case that a higher IQ makes for a happier, healthier, longer life, clearly it can’t be the only causal factor. Before we get too excited, we need also to consider the connection between social class and intelligence. We also need to see whether we’re pointing the causal arrow the wrong way round. Maybe higher social classes, with its many attendant advantages causes, higher intelligence. This is certainly plausible. The correlation between social class and IQ scores is certainly there (r=0.3-0.5) but it’s not as strong as you might expect. There’s no doubt that your background has an effect on your life chances, but there’s also evidence of a connection between higher IQ and social mobility; the cleverer you are, the more likely you are to improve your socio-economic standing. Where you start off will be an important determining factor in where you end up, but so will your intelligence.

In addition, intelligence isn’t just an individual good; it’s also a social good. Raising IQ will also make society better for everyone. The more intelligent you are, the less likely you are to commit a violent crime and, even more interesting, the less likely you are to have a violent crime committed against you or of being murdered. In his magisterial study of violence and its decline in the modern era, The Better Angels of Our Nature, Steven Pinker argues that the cleverer you are, the more likely you are to cooperate with other people, weigh the consequences of your actions and think in such a way that allows you to escape the confines of your own limited experiences. Amazingly, the more intelligent you are the lower the probability that you’ll be racist or sexist and the greater the likelihood that you’ll be socially liberal. And if all that wasn’t enough, there’s also a pretty strong connection to happiness. People who score more highly on IQ tests also tend to report being happier.

Possibly the strongest correlations with intelligence is that with educational outcomes. The higher your IQ, the more likely you are to do well in school and the longer you’re likely to stay in school. It might seem self-evident that people who score better on IQ test go on to do better a school, because educational success is predicated on measuring the same kind of ability. But, it’s worth knowing that the correlation between IQ tests taken five years previously and GCSE results taken at age 16 is one of the strongest yet found in psychology (r=0.81). The predictive power of the IQ test seems astonishingly accurate.

Accurate, but far from perfect. Before you start wondering whether we could do away with examinations in school altogether and just give a single, one hour IQ test, you need to know that some people with high intelligence did not perform well in other tests and that some people who did well in their GCSEs did poorly on an IQ test. There are, it would appear, other factors such as conscientiousness, motivation and self-control, involved in educational success. There’s also evidence that education may cause increases in intelligence.

Whatever the question is, it seems that intelligence is always at least part of the answer. If we want children to be happier, healthier, more successful, to live long and earn more, then it will pay to try to make them cleverer. So, having tried to established that IQ matters, in Part 2 of this series I’ll discuss the fact that IQ scores seem to be rising across the developed and developing world and what this suggests about intelligence, IQ testing and improving education.

Acknowledgement: I owe a huge debt to Stuart Ritchie’s wonderful little book Intelligence: All That Matters for collecting together most of the research that has informed this post.