Medusa grabs IQ from jaws of Scylla

Consider these two slices of motherhood-and-apple-pie, valedictory homilies from two recent books about human intelligence: "Each human being has strengths and weaknesses, qualities we admire and qualities we do not admire, competencies and incompetencies, assets and debits; the success of each human life is not measured externally but internally; that of all the rewards we can confer on each other, the most precious is a place as a valued citizen."

"In the recognition of our individuality, we may discover our deepest common tie - that we are all joint products of natural and cultural evolution. And we may discover why we must join forces, in a complementary but synergistic way, to make sure that nature and culture survive for future generations."

The latter quotation is from Howard Gardner's book. Despite the similarity of tone, the former quotation is from its opposite, politically speaking, The Bell Curve (by Richard J. Herrnstein and Charles Murray, 1994), the odd bestseller of the mid-1990s that warned of increasing social apartheid in the United States based on differences in general intelligence. Both books address the public, educationists and policy-makers directly about human intelligence differences, bypassing researchers.

Gardner's book avowedly provides an antidote to The Bell Curve . As a result of what he calls "the Scylla of the psychometricians" having been overcome, Gardner celebrates the diversity of human cognitive powers in a theory of multiple intelligences (MIs) that transcends the restricted demesne of the IQ-testers. However, here are some well-attested facts about human intelligence differences that are central to psychometricians' efforts and are not denied by Gardner: a general factor (often called just g) accounts for about 50 per cent of the variance in diverse human cognitive performances; there are group-ability factors and specific-ability factors besides g; psychometric intelligence has a substantial stability and heritability; psychometric intelligence has some predictive validity for educational and occupational outcomes. All this and more can be had from the authoritative and disinterested voices of the American Psychological Association's task force report on IQ ( American Psychologist , February 1996).

So, what exactly is Gardner saying that distinguishes him from the psychometricians he derogates in his essays? Sure, he wants to celebrate the richness of humans' diverse abilities and he wants to get away from what he incorrectly calls paper-and-pencil tests, but it is not always clear what he claims for his MIs. In one essay, he says the idea of MIs was: "Taking the once unitary notion of intelligence and fractionating it (one hopes) along the lines that nature intended." Elsewhere: "I do not consider the study of g to be scientifically suspect, and I am willing to accept the utility of g for certain theoretical purposes." And again: "The theory (of MIs) is simpler, both conceptually and biologically, if the intelligences are totally independent of one another. Yet, each intelligence does not have to be independent of the others, and it may turn out empirically that certain intelligences are more tied together than are others."

This vagueness supports the widely held judgement that there is insufficient operationalisation of multiple intelligences and too little empiricism. It is hard to pin down the theory's claims. This is illustrated in the essay in which Gardner admits a new "intelligence" to his list from the candidates, naturalistic, spiritual and existential. Spiritual is rejected, naturalistic is admitted, but existential is kept in a kind of Gardnerian purg-atory: half-in, half-out of the cognitive oligarchy. The chapter reveals the partly subjective and discursive method by which Gardner will "accept" an intelligence.

There is empirical evidence for cognitive abilities other than g, yet none of this research is reviewed. When Gardner discusses "existential [half-]intelligence" he fails to mention Robert Cloninger's work over the past decade that addressed this aspect of character. When Gardner addresses moral intelligence, the nugatory mention of psychopathy effectively ignores massive empirical data. And there is a worrying tone: "While I am not ready to proclaim a ninth intelligence..."

This is to misread the audience targeted by Gardner's books. They are not for me: the whingeing, picky psychometrician still working in the belly of the flailing, but doomed sea-monster Scylla. They are for people in education and the public. They will find an engaging, cultured voice that will make them comfortable concerning human abilities and achievements. Content-wise, they will find a pick 'n' mix of recycled essays. Many are about Gardner's previous writings: the original books on multiple intelligences and geniuses are better. Some essays are frequently asked questions on the theory, some describe applications and some are about the place of MI theory in the study of intelligence more generally. But the book is not a large supplement to Gardner's oeuvre ; some of it is a prequel or "the making of Frames of Mind " type of commentary.

There are good things about Gardner's ideas. He is innovative about the criteria for an "ability". He reminds us that prodigies and savants test the rule about general intelligence. He highlights areas of human potential and accomplishments beyond the traditional confines of the cognitive. But the intellectual feast provided for his many admirers leaves the scientific community of intelligence researchers empirically malnourished. Certainly, he feeds them too little to accept his grand claim that: "I put forth the intelligences as a new definition of human nature, cognitively speaking."

Ian J. Deary is professor of differential psychology, University of Edinburgh.