This survey of “primary” or first-order factors of cognitive ability found in the factor-analytic literature begins by considering factors interpreted as lying in the broad domain of language. The line between this domain and many others, such as that of reasoning, is difficult to draw. Many factors appear to depend on both language abilities and other abilities, such as reasoning and memory. I consider here the factors that appear to draw more on language abilities than other abilities. Furthermore, the tests loaded on any of a great many factors presuppose the subject's knowledge of his or her native language, either in its spoken form or – much more frequently – in its written, printed form, either in understanding instructions for these tests or in actually responding to the tasks presented in the tests. This very fact complicates the interpretation of any intercorrelations among factors and of any higher-order factors that are isolated in the analysis of test batteries (see Chapter 15). But it also justifies the consideration of factors in the language domain before all others, because it leads to establishing a kind of baseline for the consideration of those other factors.

Even the language domain itself is complex, for as this chapter shows, there are many different aspects of knowing and using a language.