Abstract: The Existential Coda Construction displays idiosyncrasies of the elements, the syntactic pattern and the discourse. Previous studies employing the syntactic approach in TG fail to uncover the interconnections and motivations of the idiosyncrasies. From the conceptual semantics and cognitive processing perspective, this paper argues that the Access and Activation Model is the cognitive mechanism, which can account for the idiosyncrasies. Furthermore, this cognitive approach not only provides a cognitive account of the Existential Coda Construction, but also proves that the Access and Activation Model can give a unified account of linguistic structure, processing, and discourses. It also offers a new perspective on the study of the Chinese“argument sharing” and English “amalgams”.