Charles Spearman had an unusual background for a psychologist. After 15 years as an officer in the British Army he resigned to study for a PhD in experimental psychology. In Britain, psychology was generally seen as a branch of philosophy and Spearman chose to study in Leipzig under Wilhelm Wundt, because Spearman had no conventional qualifications and Leipzig had liberal entrance requirements. He started in 1897, and after some interruption (he was recalled to the army during the South African War) he obtained his degree in 1906. He had already published his seminal paper on the factor analysis of intelligence (1904). Spearman met and impressed the psychologist William McDougall who arranged for Spearman to replace him when he left his position at University College London. Spearman stayed at University College until he retired in 1931. Initially he was Reader and head of the small psychological laboratory. In 1911 he was promoted to the Grote professorship of the Philosophy of Mind and Logic. His title changed to Professor of Psychology in 1928 when a separate Department of Psychology was created.
When Spearman was elected to the Royal Society in 1924 the citation read “Dr. Spearman has made many researches in experimental psychology. His many published papers cover a wide field, but he is especially distinguished by his pioneer work in the application of mathematical methods to the analysis of the human mind, and his original studies of correlation in this sphere. He has inspired and directed research work by many pupils.” Chief amongst these achievements was the discovery of the general factor in human intelligence, [and his subsequent development of a theory of “g” and synthesis of empirical work on ability.
Spearman was strongly influenced by the work of Francis Galton. Galton did pioneering work in psychology and developed correlation, the main statistical tool used by Spearman.
In statistics, Spearman developed rank correlation (1904), a non-parametric version of the conventional Pearson correlation, as well as both the widely used correction for attenuation (1907), and the earliest version of a ‘factor analysis’ . His statistical work was not appreciated by his University College colleague Karl Pearson and there was a long feud between them.
Although Spearman achieved most recognition in his day for his statistical work, he regarded this work as subordinate to his quest for the fundamental laws of psychology, and he is now similarly renowned for both.
Here, Spearman gives a compact summary of his findings and theory of g:
When asked what G is, one has to distinguish between the meanings of terms and the facts about things. G means a particular quantity derived from statistical operations. Under certain conditions the score of a person at a mental test can be divided into two factors, one of which is always the same in all tests, whereas the other varies from one test to another; the former is called the general factor or G, while the other is called the speciﬁc factor. This then is what the G term means, a score-factor and nothing more. But this meaning is sufﬁcient to render the term well deﬁned so that the underlying thing is susceptible to scientiﬁc investigation; we can proceed to ﬁnd out facts about this score-factor, or G. We can ascertain the kind of mental operations in which it plays a dominant part as compared with the other or speciﬁc factor. And so the discovery has been made that G is dominant in such operations as reasoning, or learning Latin; whereas it plays a very small part indeed in such operation (sic) as distinguishing one tone from another. . . G tends to dominate according as the performance involves the perceiving of relations, or as it requires that relations seen in one situation should be transferred to another. . . . On weighing the evidence, many of us used to say that this G appears to measure some form of mental energy. But in the ﬁrst place, such a suggestion is apt to invite needless controversy. This can be avoided by saying more cautiously that G behaves as if it measured an energy. In the second place, however, there seems to be good reason for changing the concept of energy to that of “power” (which, of course, is energy or work divided by time). In this way, one can talk about mind power in much the same manner as about horse power. . . . . . .G is in the normal course of events determined innately; a person can no more be trained to have it in higher degree than he can be trained to be taller.
There was also another co-factor as proposed by Spearman that was special intelligence. The special intelligence was for individuals who accomplished high success results in the some tests. However, later Spearman introduced group factor that was particular to those correlations that were not a result of factor g or s. His ideas were in 1938 criticized on paper by Louis L. Thurstone a psychologist saying that his experiments show that the correlation of intelligence can be categorized in seven primary categories. These categories were numerical, reasoning, spatial, perceptual, memory, verbal fluency and verbal comprehension. However Raymond B. Cattell in 1963 agreed with the concept theorized by Spearman but put forth his findings about intelligence analyses. His analyses were that intelligence is further subdivided in two divisions known as fluid and crystallized intelligence.
As time progressed, Spearman increasingly argued that g was not, from a psychological point of view, a single ability but composed of two very different abilities which normally worked closely together. These he called “eductive” ability and “reproductive” ability. The former term comes from the Latin root “educere” – which means to “draw out” and thus refers to the ability to make meaning out of confusion. He claimed that to understand these different abilities “in their trenchent contrast, their ubiquitous cooperation, and their genetic interlinkage” would, for the study of “individual differences – and even cognition itself” – be “the very beginning of wisdom.
Despite Spearman arguing that g was what emerged from a large battery of tests, i.e., that it was not measured perfectly by any single test, the fact that g-theory suggested that much of ability could be captured in a single factor, and his suggestion that “the eduction of relations and correlates” underlay this general factor led to the quest for tests of this general ability. Raven’s Progressive Matrices might be regarded as one of these although Raven himself clearly stated that his tests should not be regarded as “intelligence” tests.
While arguing consistently that g accounted for much of individual differences in “ability” (as measured by tests which had “no place in schools”), Spearman also acknowledged that “Every normal man, woman, and child is … a genius at something … It remains to discover at what …” He thought that detecting these areas of genius required procedures very different from “any of the testing procedures at present in current usage”, though he felt these to be capable of “vast improvement”.