Gall's psychophysiological concept of function: the rise and decline of "internal essence".

Gall did not employ the term "function" to refer to adaptive mental processes or to observable behavior. To the contrary, he and the phrenologists took a traditional concept of function regarding the contribution or duties of a part within the overall "animal economy" and argued that the "faculties" of the soul are among the functions of the nervous system. In particular, he brought this psychophysiological use of the term into his Enlightenment perspective when he aligned it with internal essence, juxtaposed it to its external sign, and argued that the cerebral organs are the material instruments through which the internal faculties manifest themselves in behavior and in the shape of the skull. Gall did not believe that the faculties are a product of the organs but that the organs, being material incarnations of the internal functions, contain the power to express the faculties externally. Purely psychological uses of function are infrequent among the works of Gall and his followers. It was not until the functionalists at the turn of the century that the word was applied to the adaptive utility of mental processes in relation to the environment and not until the advent of behaviorism that it was employed to refer to the end or adaptive utility of a particular behavior.