本文旨趣並非根據文獻論定繫詞「是」產生的年代，而是從語言表達的角度解釋複指代詞「是」的語用功能，並循有關思路說明「是」由代詞向繫詞轉化的動因。為「是」的代詞性、繫詞性及其使用條件作出一個統整的解釋。

This article is not focused on the dating of shi’s emergence as a copula; rather, it illustrates how shi has changed from a deictic substitute to a copula from the perspective of information structure, bringing in the consideration of pragmatics. This article also provides an integral explanation on the various functions of shi as a deictic substitute, a copula, and the conditions of its usage.