Forms and Functions of Copulas： A Study on Nominal Predicate Sentences
前人对系词的认识,大致有“连接说”“傀儡说”“谓词说”三种观点。这些观点都有局限,特别不适用于汉语。本文从共时和历时的角度,跨语言描写系词隐现的规律,从而揭示系词的功能并解释名词谓语句,得知系词的作用是标明或强调“话题-述题”关系,即“增强标述性”功能。词类句法语法化程度较高的语言（如英语）,系词是语法性质的、刚性的,语法上规定了系词是否出现;词类句法语法化程度较低的语言（如汉语）,系词是语用性质的、柔性的,“话题-述题”关系是否明确或是否需要强调,决定是否出现系词。Theories on the functions of copulas normally include Linker Hypothesis, Dummy Hypothesis and Predicatot Hypothesis, all of which have their limitations, especially when applied to Chinese. In a cross-linguistic perspective, the present paper describes the copulas synchronically and diachronically, revealing that the functions of copulas are to indicate or emphasize the interpretation of ＂topic-comment＂, i. e. predicate-indicator. Copulas are obligatory in more grammaticalized languages （such as English） , and thus they are called grammatical copulas. In less grammati- calized languages （such as Chinese）, the interpretation of ＂topicomment＂ relation resorts to context and world knowledge. Copulas in these languages are optional and are thus called pragmatic copulas.