A Gaggle of <i>G</i> s: The Thomson-Spearman Dispute

Charles Spearman and Godfrey Thomson had a long disagreement about the nature of cognitive abilities. Most of the running was made by Thomson, who explicitly doubted that the g factor was anything more than a mathematical artefact, explainable by “the laws of chance alone”, on the basis of deductions made from a “bond sampling” model of the mind. Spearman believed from the start that Thomson’s arguments were contrived and disputed the conclusions he drew from them, especially his use of “chance”. Close inspection reveals that the “bond sampling” that Thomson proposed would require an oracle, and shows that his arguments from “chance” are truisms reflecting the assumptions made by the model. That model is a purely illustrative vehicle only. For that reason Thomson explicitly disavowed any commitment to the idea that it was an accurate description of how the mind physically operates. Examined closely it reduces to a restatement of Spearman’s ideas from a different starting point.