ABSTRACT
Current notions of intelligence have changed tremendously in yet another respect over the past half-century or so. We realise that mental abilities are much too varied to be adequately described in terms of a monolithic general intelligence or Spearman's g-factor. There are many more specialised types of ability — verbal, numerical, spatial and perceptual, memorising, reasoning, mechanical, imaginative and so on, and the same individual may well be quite high in one, low in another, although on the whole they tend to correlate positively. However there is some divergence of views between British and American factor psychologists regarding the number of these ability factors and their distinctiveness (cf. Vernon, 1965b). Thurstone, Guilford and their followers in the USA tend to break down the mind into a very large number of independent primary abilities or faculties, while admitting that these sometimes overlap, i.e. that there are also more general or ‘second-order’ factors. This is a legitimate model when dealing with highly selected or homogeneous groups such as university students. But British writers have been more concerned with representative samples of adults or with whole age groups of children, and when these are tested the correlations between quite different tests tend to be so high that it seems more logical to recognise a common underlying component or g, and to regard the more specialised abilities as subsidiary group factors. In other words we can picture the mind as a kind of hierarchy or genealogical tree, where the g-factor is the most prominent component in the sense that it accounts for the greatest proportion of differences in abilities (Fig. 1).
