But first he joined the army as a regular officer of engineers in August 1883,[1] and was promoted to captain on 8 July 1893, serving in the Munster Fusiliers.

As Wundt was often absent due to his multiple duties and popularity, Spearman largely worked with Felix Krueger and Wilhelm Wirth, both of whom he admired.

[1] He started in 1897, and after some interruption (he was recalled to the army during the Second Boer War, and served as a Deputy Assistant Adjutant General from February 1900[7]) he obtained his degree in 1906.

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.

Charles Spearman always insisted that his work be applied in psychiatry and urged so in his Maudsley lecture to the Royal Medico-Psychological Association.

While some work has been made on these lines by pupils and associates of his, the development of factor analysis as a tool of psychiatry followed a different path than he had intended.

[1] A record of Spearman's views on g (and also those of Godfrey Thomson and Edward Thorndike) was made in the course of the Carnegie-sponsored International Examinations Inquiry Meetings.

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.

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 factor.

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 psychologist Louis L. Thurstone who argued his own experiments showed that intelligence formed seven primary categories: numerical, reasoning, spatial, perceptual, memory, verbal fluency and verbal comprehension.

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".

[14] Spearman felt that though g could be detected in any sufficiently-broad set of cognitive measures, he felt that the tests from which his g had emerged "had no place in schools" because they "deflected" teachers', pupils', parents' and politicians' attention from the business of education which, as the Latin root of the word implies, should be concerned with "drawing out" whatever talents a student may have.

[citation needed] He presented a digest of his views in the entry "Abilities, general and special" in the 14th edition of the Encyclopaedia Britannica.

Factor analysis is a statistical test that is used to find relationships between multiple correlated measures and Spearman played a clear part in its development.

Spearman coined the term factor analysis and used it extensively in analyzing multiple measures of cognitive performance.