Asked by: Noah Sprent, by email
This is a very controversial question. Everyone knows that some people seem a lot cleverer than others, and it’s easy to imagine there must be some underlying factor called ‘intelligence’ that varies. Yet psychologists have been trying to measure intelligence and discover what it is for over a century, and they’re still arguing.
One problem is that you need some idea of what you mean by intelligence before you can design tests for it – and your ideas of intelligence might be different from those of people with a different educational or cultural background.
Some worry that intelligence is nothing more than ‘what IQ tests measure’. In other words, it doesn’t really exist. On the other hand, people’s scores on IQ tests correlate highly with all sorts of real-life measures, such as exam scores, occupational success and even sporting and musical ability.
So IQ tests measure something, but what exactly? Some psychologists argue that there is one basic kind of intelligence that underlies the rest. This is referred to as ‘g’ for general intelligence. Others insist there are many different intelligences – including social, musical and mathematical ability. For example, Howard Gardner has proposed nine types of intelligence, which can all be separately tested. You might say intelligence is one, none or all of these.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.