In the same way that it is obvious that humans are more intelligent than animals, in that they have enhanced capacity for interacting with their environment, it is also apparent that some people are more intelligent than their peers. Some people seem much better at certain tasks. They are more capable of manipulating information; more readily see the solutions to problems; are more expressive; more capable of learning. It is tempting, for all manner of reasons, to try to measure these differences.

In the 19th century, intelligence was seen as essentially a mechanical process whose effectiveness was determined by physical characteristics such as brain size, and quantified by measurement of such factors as speed of response, judgement, auditory and visual acuity.

The modern approach to intelligence began with the work of Alfred Binet who was hired by the Paris school system at the onset of the 20th century to develop tests which would identify which students were most (and least) likely to benefit from further schooling. Binet devised a barrage of tests which sought to comprehensively assess physical, mental, moral and social skills. These tests were later cannibalised to form the Stanford-Binet tests that formed the platform of much of US school assessment.

Spearman (1904) argued that there was a correlation between this diverse range of abilities, which suggested that there was a general factor (g) which influenced performance. For the greater part of the next century, much of the debate polarised along two directions.

Firstly, whether intelligence is a single factor or, if not, how many factors there are and how they interact. Thurstone (1940) proposed that there were 5 Primary Mental Abilities (word fluency; verbal comprehension; spatial visualisation; perceptual speed; memory and reasoning) whereas Guilford (1967), perhaps because of the advent of factor analysis and variance analysis, advocated no fewer than 120 separate mental abilities.

The second debate focused on whether our intelligence is determined by our genetic blueprint - or to what extent it is malleable and influenced by upbringing and societal factors. The waters of this nature / nurture debate have been muddied by the tendency of its participants (of either persuasion) to rely upon IQ as the sole measure of intelligence.

Modern scanning techniques have allowed increasingly detailed investigation of the brain's capacities, such that it is now possible to identify specific localised areas for hundreds (and eventually thousands) of particular abilities. This localisation forms a plank in Gardner's argument. Although Gardner is usually attributed with proposing 7 (or, more recently, 8 or 9) intelligences, he would probably concede that this is merely an approximate mapping of the territory. In reality, it is impossible to draw precise boundaries between one domain of intelligence and another. However, in the same way that cartographers draw maps on the basis of cultural and historical factors as well as merely geomorphic features, so it is with those who seek to chart intelligence.

Gardner's argument for choosing 7 (8 or 9) intelligences is a pragmatic one - in that it generates a model that is useful without being cumbersome. Gardner and his followers would readily concur that the theory can do little more than represent the rich portrait that is human experience as a painting by numbers: but that is considerably more useful than painting with the single number that is IQ.