Abstract
Through a CP projection, a sentence can be expanded to host such elements as WH and topic words and to become an embedded clause. However, it is not well explained why CP has such a dual nature. This article shows that the multilayered structure of CP and the diachronic change from parataxis into subordination can be explained under the hypothesis of the emergence of a functional category. More specifically, it explains why a functional category emerged in the early stage of proto-languages and how it developed into split CP projections and how subordination was grammaticalized in the course of diachronic change.
