As a fundamental design feature, language has two subsystems, the
open-class (lexical) and the closed-class (grammatical). These
subsystems perform complementary functions. In the total meaning
expressed by any portion of discourse, the open-class forms contribute
the majority of the content, while the closed-class forms determine the
majority of the structure. Further, across languages, all closed-class
forms are under great semantic constraint: They represent only certain
concepts and categories of concepts, but not others. Closed-class
representations accordingly appear to constitute the fundamental
conceptual structuring system of language. This talk will examine
some of the main conceptual categories and member concepts represented
by closed-class forms; the properties that distinguish such
closed-class representations from open-class representations; and the
conceptual structuring function performed by this organization of
language. This linguistic structure will be brought into relief by
contrasting it with the structure found in another cognitive system,
visual perception. It will be seen that language and vision, along
with other cognitive systems, each have certain structural properties
of their own and others that they share, in what I term the overlapping
systems model of cognitive organization.