It is a common presumption that if people know a lot, they must be intelligent. Anyone who can reel off capital cities or count to 10 in several languages – or, in the case of a two-year-old girl heralded in newspapers this week, tell an apple from a banana early enough – is counted a bright spark. And often enough intelligence, a good memory and a well-informed mind go together because intelligence prompts curiosity, curiosity results in knowledge, and memory keeps the knowledge available.
But there is no automatic connection between knowledge and intelligence. There are plenty of very bright people who do not know the world's capitals and cannot count in other languages, because they have never had a chance to learn them. In rural Africa there must be millions of smart kids who know nothing but local lore; they are Thomas Grey's "village Hampdens" and "mute inglorious Miltons".
By the same token plenty of people know lots of facts without being creative, thoughtful, quick-witted, humorous and perceptive – the marks of true intelligence. Sometimes an overload of facts is the mark of a dull and pedestrian mind, the antithesis of intelligence.
Moreover, there are different kinds of intelligence, better described as different gifts of mind, so that a person can be wonderfully talented in one respect and hopeless in another. It is misleading to describe anyone as intelligent without specifying what form the intelligence takes. Some mental aptitudes are hard-wired: gifts for maths and music (which often go together) require no knowledge, and manifest themselves early in life. So does artistic ability. Many autists have extremely high-order talents in these respects without acquiring any knowledge, or even interacting much with other people.
But other aptitudes require training, data, experience and practice. Here intelligence and a body of knowledge meet, and the former acts on the latter in productive ways. One can train a parrot to reel off English kings and queens, but it takes an accomplished historian to tell us insightful things about them.
"Intelligence tests" have always been a matter of controversy. Practice improves scores, which raises a question mark over whether they capture anything objective. If someone scores high on verbal tests and low on spatial ones, what does that overall score tell us about the individual in question? Nothing very informative.
There are many "high IQ" societies, the best-known being Mensa, which admits people with IQs in the top 2% of the population. At Mensa's 50th anniversary in 1996 one of the founders, Lancelot Ware, said he regretted the fact that members devoted far more time to puzzles than improving the world.
That prompts a thought: intelligence is a matter of output, not scores in a test. Einstein was unsuccessful at school and no great shakes as a mathematician, but he was creative and insightful, and saw a whole new way of thinking about gravity and the structure of space-time. A vivid interest in things, and an active desire to understand more about them, is a major characteristic of intelligence. When this leads to great creativity and important discoveries, we call it genius.
In the ancient world a genius was a creature who whispered ideas, ambitions and insights into your ear. The Romantics internalised genius, identifying it with their own inner selves – what Proust called le moi profond, the deepest me. As there are many kinds of achievement, so there are many kinds of genius suited to them. To all, the wonderful old cliche about 99% perspiration applies.
IQ tests rarely predict achievement or correlate with knowledge, and they are too blunt an instrument to capture the variety of human gifts. The latter are what matter. As with everything else, we know these gifts by their fruits, not by artificial ways of defining them.
AC Grayling