This paper takes the corpus-based approach to conduct a case study concerning the interaction between discourse and grammar and offer support from Chinese to the hypothesis that grammaticalization is a result of daily, routinized use of language. In particular, two related Chinese expressions, jiushi and jiushishuo (and their reduced from, jiushuo) are examined for their respective uses in speech as compared with in writing and their collocation with prosodic and discourse features characteristic of conversation. We argue that grammaticalization for the expression, jiushi, is currently on-going, in which the copula sense of the expression is first reduced to a connective marking textual coherence. This semantic "reduction" is developed with the help of jiushi's collocation with the verb of saying, shuo. Then, the connective sense becomes semantically even "emptier" when jiushi and jiushishuo serve as pause fillers in interactive speech. Again, their contiguity with intonation unit boundaries, continuing intonational breaks, and other discourse markers in speech may have led to this semantic "reduction". The case study not only shows that repeated daily language use is where early stages of grammaticalization take place, but also supports the hypothesis that linguistic contiguity is one of the important sources leading to the inception of grammaticalization.