We’ve written about this before in More Urban Myths about Learning and Education and The Psychology of Great Teaching, but I keep being struck by how often the same misconceptions about intelligence resurface. Then again, perhaps that’s not surprising. Intelligence and intelligence research have been provoking strong reactions for well over a century, something I have occasionally experienced myself. Some people treat IQ as if it explains almost everything, while others dismiss it as little more than a social construct. As so often, the reality is more nuanced, and that nuance is worth repeating.

Let me start with something almost everyone agrees on. An IQ score says nothing about a person’s worth. It tells us nothing about kindness, creativity, perseverance, or moral character. Someone with an average IQ can become an outstanding nurse, entrepreneur, or teacher. Someone with a very high IQ can be a terrible colleague. I’ve met wonderful people and awful people at every level of intelligence. Intelligence tests were never designed to measure any of those qualities.

Yet this is where people often take a wrong turn. Once they accept that IQ does not tell the whole story about a person, some jump to the conclusion that intelligence itself does not exist. The evidence says otherwise. Psychologists have repeatedly found that people who perform well on one cognitive task also tend to perform well on many others. Researchers first described this pattern more than a century ago, and thousands of studies have confirmed it since. Psychologists call it the positive manifold: the tendency for different cognitive abilities to correlate positively with one another. Today, researchers no longer debate whether this pattern exists. Instead, they debate how best to explain it.

That does not make intelligence simple. Modern intelligence tests no longer boil cognition down to a single number. Instead, they measure a range of abilities, including working memory, processing speed, verbal comprehension, and fluid reasoning. The familiar IQ score simply summarises a much richer cognitive profile.

Another common misunderstanding concerns heredity, a topic we discuss extensively in Almost Everything You Need to Know About Psychology. It is also one of the most misunderstood concepts in psychology. When psychologists say that intelligence is partly heritable, they do not mean that education or upbringing are unimportant. Heritability does not mean immutability. Genes and environments constantly influence one another. High-quality education can foster cognitive development, while a deprived environment can hold it back.

Perhaps the more intelligent question (pun intended) is not whether IQ exists, but what we actually need it for. For teachers, the answer is surprisingly simple: usually not much. A good teacher looks at what a student knows, understands, and can do. Tests, observations, and other forms of formative assessment generally provide far more useful information than an IQ score. You do not help a student struggling with fractions by knowing their IQ. You help them by understanding where the learning process has broken down and responding accordingly.

That does not mean IQ belongs in the history books. It can still be valuable for identifying intellectual disabilities, recognising giftedness, or contributing to a broader psychological assessment. Like any measurement tool, it has a specific purpose. A thermometer is not useless simply because it cannot measure blood pressure.

What concerns me is the significance we sometimes attach to IQ in public debate. A high score does not make someone more valuable. A low score does not make someone less important. Society needs people who can program, weld, teach, nurse, research, design, and care. Those contributions are different, but they are no less valuable because they require different strengths.

One final misconception stubbornly refuses to disappear. The theory of multiple intelligences is often presented as a scientific alternative to IQ, but that was never really its purpose. There is little empirical evidence that the different “intelligences” proposed by Howard Gardner exist as distinct cognitive abilities in the way the theory suggests. Gardner himself has acknowledged that the theory was never intended as a psychometric model and has not been validated in the same way as mainstream intelligence research.

There’s much more to say about intelligence, but this is a blog, not a book. Fortunately, Stuart Ritchie has already written that book.