A new lease of life for Thomson's bonds model of intelligence.

Modern factor analysis is the outgrowth of Spearman's original "2-factor" model of intelligence, according to which a mental test score is regarded as the sum of a general factor and a specific factor. As early as 1914, Godfrey Thomson realized that the data did not require this interpretation and he demonstrated this by proposing what became known as his "bonds" model of intelligence. Van der Maas et al. (2006) have recently drawn attention to what they perceive as difficulties with both models and have proposed a 3rd model. Neither alternative requires the general factor that was at the core of Spearman's idea. Although Thomson's model has been largely forgotten, the authors show that it merits further consideration because it can compete, statistically and biologically, on equal terms with Spearman's model. In particular, they show that it is impossible to distinguish statistically between the 2 models. There are also lessons to be learnt from the way in which Thomson arrived at his model and from the subsequent debate between Spearman and Thomson. The extent to which the recent proposal by van der Maas et al. may offer any advantage over Spearman's and Thomson's models is unclear and requires further investigation.