modularity the commitment to functionally independent and specialized cognitive systems in psychological organization, or, more generally, in the organization of any complex system. Modularity entails that behavior is the product of components with subordinate functions, that these functions are realized in discrete physical systems, and that the subsystems are minimally interactive. Modular organization varies from simple decomposability to what Herbert Simon calls near decomposability. In the former, component systems are independent, operating according to intrinsically determined principles; system behavior is an additive or aggregative function of these independent contributions. In the latter, the short-run behavior of components is independent of the behavior of other components; the system behavior is a relatively simple function of component contributions.
In the early nineteenth century, Franz Joseph Gall (1758–1828) defended a modular organization for the mind/brain, holding that the cerebral hemispheres consist of a variety of organs, or centers, each subserving specific intellectual and moral functions. This picture of the brain as a collection of relatively independent organs contrasts sharply with the traditional view that intellectual activity involves the exercise of a general faculty in a variety of domains, a view that was common to Descartes and Hume as well as Gall’s major opponents such as Pierre Flourens (1794–1867). By the middle of the nineteenth century, the French physicians Jean-Baptiste Bouillaud (1796–1881) and Pierre-Paul Broca (1824–80) defended the view that language is controlled by localized structures in the left hemisphere and is relatively independent of other cognitive activities. It was later discovered by Karl Wernicke (1848–1905) that there are at least two centers for the control of language, one more posterior and one more anterior. On these views, there are discrete physical structures responsible for language, which are largely independent of one another and of structures responsible for other psychological functions. This is therefore a modular organization. This view of the neurophysiological organization of language continues to have advocates into the late twentieth century, though the precise characterization of the functions these two centers serve is controversial. Many more recent views have tended to limit modularity to more peripheral functions such as vision, hearing, and motor control and speech, but have excluded so-called higher cognitive processes. See also COGNITIVE SCIENCE, PHILOSOPHY OF MIN. R.C.R.