This article mainly discusses the adverb kě "可" and a type of sentences with kě in which at least some elements preceding ki are phonetically stressed. It identifies this "modal adverb" as a topical focus sensitive operator (TFSO), which makes the clause with kě a topic structure, indicating that some preceding part in the clause is a "topical focus" (topic-F), in contrast with some element existing in the background information or presupposition. In addition, the paper examines the topical focus sensitive operator kě in real text, revealing the variety of its usage and, more importantly, its unified nature as an operator behind the variety.