Duncan's theory allows that executive function may be represented by a central and general construct of intelligence which was originally described by Spearman (Spearman, 1946). This theoretical critique discusses the three planks of evidence which appear to support this proposal: (1), the finding that intra correlations between “executive” tests are low and in one study equivalent to those with non-executive tasks, (2), that tests which are seen as most representative of Spearman's G may be used to identify patients with frontal lobe lesions and executive dysfunction and (3), the finding that functional neuroimaging studies which have used disparate tasks may show a similar region of activation within the prefrontal cortex. The evidence for these three findings is discussed in terms of their ability to support Duncan's theory.