This paper examines the usage of NE in Chinese dialogues and monologues excerpted from a Chinese collection of narratives. The analysis of NE as a constituent in discourse structure shows that linguistically it functions like a grammatical connector. From a cognitive point of view, NE signals topic shift and focuses on new, contrastive information. It is argued that coherence is achieved through semantic contrastiveness, and pragmatic relevance. It is also argued that the prosodic feature of pause i.e. NE+{Pause}, serves to further emphasize the semantic contrastiveness in topic and comment. Coherence is defined not merely in terms of structural relations but more importantly from the viewpoint of semantic connectivity. It is the focus on semantic connectivity signaled by NE, which underlies the semantic cohesion in topic shifts.