Research has shown that we often do this on the basis of the most fleeting of information, such as language dialect, personal demeanour, or even physical height and facial appearance. This kind of thing goes on in all known societies.
But we're still very unclear about what the concept is a concept of. When people in the street are asked about the attributes of intelligence we get a phenomenal diversity of responses. The same applies to the use of the term in the media, in popular writing, and so on. According to my thesaurus of synonyms, if you have intelligence then you also have common sense, nous, wits, grey matter, gumption, horse sense.
At the same time, most people have little doubt about the importance of intelligence in just about every domain - school, work, marriage, family life, social life and life in general. When asked what characteristics they most want their children to have, would-be parents all too often suggest beauty and intelligence. And there's nothing more maddening than people who end up with both - or think they have done so. In addition, psychologists and most other people seem to have little doubt about where it comes from.
In the world of designer babies, which some argue is just around the corner, IQs of donors figure prominently on the labels on the test-tubes. Indeed, sperm banks are now being set up in various parts of the world. And they're hunting for high-achieving men who will attend and earn a small fee.
And all this, of course, opens up other, very serious, issues. By being connected with biological determinism in this way, the idea of intelligence becomes bound up with big ideological and political issues such as social inequality, access to opportunity, the right to privilege, acceptability of poverty and exploitation, even the right to life itself.
We all know the horrors to which that "bio-logic" has sometimes led this century. And, because of this, it's often difficult to even mention the subject of intelligence without getting someone's back up.
I start, probably inevitably, with IQ. Most people feel secure with the notion of IQ and accept it as a rough measure of intelligence. And not just of current performance, but of innate potential for intelligence. In convincing most people that the test is a fair and valid instrument of that sort, IQ testers have won a tremendous propaganda battle. They claim that IQ measures a single, and entirely hypothetical, mental energy or power, which they call "g", and which sums up a person's permanent potential for intelligence in one neat, single score.
My argument is that the IQ test is not an objective, scientific instrument at all. Indeed, what most people don't realise is that the IQ test is a most peculiar kind of instrument. It isn't like measuring your blood pressure by observing the height of a column of mercury, or checking your blood-alcohol level from the colour of light in a breathalyser, or checking your level of infection by a white cell count.
In each of these proper scientific instruments we have a clear understanding of the connection between the visible index on the outside and what - on the inside - has in fact produced it.
With intelligence and IQ there is no such clearly worked-out connection: we end up with an external score without knowing what the internal quantity it's supposed to represent really is.
An IQ score is not a measure of any general cognitive competence at all; it simply measures individuals' proximity to a specific culture - that of the test designers, and of school learning. Perhaps the best piece of evidence for that argument is the fact that average IQ scores in every country where testing has gone on have increased relentlessly over the last 50 years, in some cases by 15 percentage points.
This is an enormous puzzle among the IQ-testing community because it would not, of course, be expected from a test of an innate, fixed power. But it does correspond with significant swelling of the middle classes in all countries over the same period.
Developed human intelligence is a wonderful thing to behold, the most complex and dazzling product of living processes. Yet almost everywhere we look we find it suppressed. This is the damaging consequence of the IQ model of intelligence. The whole model is psychologically vacuous and biologically highly naive.