系词

系词（copula、复数为copulas或copulae、英文简称cop），又译为-{zh-hans:系动词、联系动词; zh-hant:系动词、联系动词}-，在语言学为表示用于与谓词（主语补语）链接句子之主词的字词，比如在句子「The sky is blue.」的单词「is」 。系词源于拉丁语名词为「链接（link）」或「结合（tie）」两件不同「事（thing）」之功能语词。
系词往往是动词或「类动词」（verb-like）的字词，虽然这不是普遍的情况。动词如为系词有时称为「系辞」（copulative）或「连系动词」（copular verb）。在英语初等教育语法教学的课程，一个系动词通常称为「连系动词」（linking verb）。在其他语言中，系动词表现出更多相似于代词之处，如古典汉语文言文及瓜拉尼语。或表现为名词后缀的形式，比如在贝哈语（Beja language）、凯特语，和爱斯基摩－阿留申语系里的应用。
大多数语言都有一个主系词（虽然有些像西班牙语、葡萄牙语，及泰语等语言有多个系词或者没有系词）。在英语、系词是动词<"to be">。而这术语“系词”（系动词）一般是用来说明像“联系”这样的主要涵义，它也可以广义地包含其他动词，例如英语的“成为”（become）、“得到”（get）、“感觉”（feel）等（这些用法也可称为「半系词」（semi-copulas）或「准系词」（pseudo-copulas））。
特定的语言的系词.
英语.
英语的系动词"be"有八种形式（超过任何其他英语动词）："be", "am", "is", "are", "being", "was", "were", "been"。其他古代形式包括"weren", "art", "wast", "wert"有时用"beest"（作为虚拟语气）。更多细节参见英语动词。对于各种形式的词源，见印欧语系词。
上文中描述了英语系词的主要用途。在零系词下提到系词省略的可能性。
英语中有一个特殊用法（特别是在演讲中），就是只需要一个系词的地方但两个系词连续出现，比如"My point is, is that..."。这种结构的可接受性是英语语法中的一个争议。
简单的英语系词“be”有时可以用具有接近相同含义的其他动词替代；jest'", even though the Germanic, Italic and Slavic language groups split at least 3000 years ago. The origins of the copulas of most Indo-European languages can be traced back to four Proto-Indo-European stems: "*es-" ("*h1es-"), "*sta-" ("*steh2-"), "*wes-" and "*bhu-" ("*bʰuH-").
格鲁吉亚语.
As in English, the verb "to be" ("qopna") is irregular in Georgian (a Kartvelian language); different verb roots are employed in different tenses. The roots -"ar"-, -"kn"-, -"qav"-, and -"qop"- (past participle) are used in the present tense, future tense, past tense and the perfective tenses respectively. Examples:
Note that, in the last two examples (perfective and pluperfect), two roots are used in one verb compound. In the perfective tense, the root "qop" (which is the expected root for the perfective tense) is followed by the root "ar", which is the root for the present tense. In the pluperfective tense, again, the root "qop" is followed by the past tense root "qav". This formation is very similar to German (an Indo-European language), where the perfect and the pluperfect are expressed in the following way:
Here, "gewesen" is the past participle of "sein" ("to be") in German. In both examples, as in Georgian, this participle is used together with the present and the past forms of the verb in order to conjugate for the perfect and the pluperfect aspects.
罗曼斯语.
Copulas in the Romance languages usually consist of two different verbs that can be translated as "to be", the main one from the Latin "esse" (via Vulgar Latin "essere"; "esse" deriving from "*es-"), often referenced as "sum", another of the Latin verb's principal parts), and a secondary one from "stare" (from "*sta-"), often referenced as "sto", another of that Latin verb's principal parts. The resulting distinction in the modern forms is found in all the Iberian Romance languages, and to a lesser extent Italian, but not in French or Romanian. The difference is that the first usually refers to essential characteristics, while the second refers to states and situations, e.g., "Bob is old" versus "Bob is well". A similar division is found in the non-Romance Basque language (viz. "egon" and "izan"). (Note that the English words just used, "essential" and "state", are also cognate with the Latin infinitives "esse" and "stare". The word "stay" also comes from Latin stare, through Middle French "estai", stem of Old French "ester".) In Spanish and Portuguese, the high degree of verbal inflection, plus the existence of two copulas ("ser" and "estar"), means that there are 105 (Spanish) and 110 (Portuguese) separate forms to express the copula, compared to eight in English and one in Chinese.
In some cases, the verb itself changes the meaning of the adjective/sentence. The following examples are from Portuguese: 
斯拉夫语.
Some Slavic languages make a distinction between essence and state (similar to that discussed in the above section on the Romance languages), by putting a predicative expression denoting a state into the instrumental case, while essential characteristics are in the nominative. This can apply with other copula verbs as well (e.g. the verbs for "become" are normally used with the instrumental).
As noted above under , Russian and other East Slavic languages generally omit the copula in the present tense.
爱尔兰语.
In Irish and Scottish Gaelic, not only are there two copulas but the syntax is also changed when one is distinguishing between states or situations and essential characteristics. Describing the subject's state or situation typically uses the normal VSO ordering with the verb "bí". The copula "is" is used to state essential characteristics or equivalences.
In Irish, the copula is used for things that are in a permanent state. 
The word "is" is the copula (rhymes with the English word "hiss"). 
The pronoun used with the copula is different from the normal pronoun. For a masculine singular noun, "é" is used (for "he" or "it"), as opposed to the normal pronoun "sé"; for a feminine singular noun, "í" is used (for "she" or "it"), as opposed to normal pronoun "sí"; for plural nouns, "iad" is used (for "they" or "those"), as opposed to the normal pronoun "siad".
To describe non-permanent states, "to be" is used, e.g., "Tá mé ag rith" "I am running".
海地克里奥尔语.
Haitian Creole, a French-based creole language, has three forms of the copula: "se", "ye", and the zero copula, no word at all (the position of which will be indicated with "Ø", just for purposes of illustration).
Although no textual record exists of Haitian-Creole at its earliest stages of development from French, "se" is derived from French (written "c'est"), which is the normal French contraction of (that, written "ce") and the copula (is, written "est") (a form of the verb "être").
The derivation of "ye" is less obvious; but we can assume that the French source was ("he/it is", written "il est"), which, in rapidly spoken French, is very commonly pronounced as (typically written "y est").
The use of a zero copula is unknown in French, and it is thought to be an innovation from the early days when Haitian-Creole was first developing as a Romance-based pidgin. Latin also sometimes used a zero copula.
Which of "se" / "ye" / "Ø" is used in any given copula clause depends on complex syntactic factors that we can superficially summarize in the following four rules:
1. Use "Ø" (i.e., no word at all) in declarative sentences where the complement is an adjective phrase, prepositional phrase, or adverb phrase:
2. Use "se" when the complement is a noun phrase. But note that, whereas other verbs come "after" any tense/mood/aspect particles (like "pa" to mark negation, or "te" to explicitly mark past tense, or "ap" to mark progressive aspect), "se" comes "before" any such particles:
3. Use "se" where French and English have a dummy "it" subject:
4. Finally, use the other copula form "ye" in situations where the sentence's syntax leaves the copula at the end of a phrase:
The above is, however, only a simplified analysis.-->
日语.
日语系词（在国文法中认为是助动词的一部分）最常翻译为英语的「be」动词。
日语系词有许多形式。「だ」和「です」两个词用于判断句，而「な」和「で」是在句子中用于修饰或连接的助词。
有系词的日语句子通常是在给一个事物与另一个事物画等号，也就是说，形式如同“A是B”。例子：
「だ」和「です」的区别很简单。「です」比「だ」更正式而尊敬。因此，许多句子如下面的句子在意义上几乎是相同的，它们的不同点在于说话者对听者的尊敬，以及他们对陈述的肯定程度上的细微差异。但「です」永远不会在句子结尾之前，「だ」仅用于描述从句。
日语中可以用系词或动词来形成判断句。但是，「です」不是所有时候都是谓语。在某些情况下，它的唯一作用是让用静态动词作谓语的句子更有礼貌。不过，「だ」总是充当谓语，因此它不能与静态动词结合，因为句子只需要一个谓语。参见下面的例子。
「です」的起源有若干理论；其中一论是说它是（的礼貌形式）。一般来说，这两种形式只用于写作和更正式的情况。另一种形式比「であります」更正式，其词源是接续敬语语尾，也在一些情况下使用，非常有礼貌。注意有人认为「である」和「でござる」是助词与存在动词「ある」和「ござる」结合而成的。口语可能会读成。系词在日本各地受到方言变化的影响，形成诸如关西的和广岛的（见右图）。
日语还有两个对应于英语“to be”的动词「ある」和「いる」。它们不是系词而是存在动词。「ある」用于无生命物体，包括植物，而「いる」用于有生命物体，如人、动物和机器人，但也有例外情况。
日本人在学英语时常把助动词「be」或「do」丢掉，误认为「be」与「です」和「だ」一样语义是空系词。
汉语.
在汉语中，状态和品质一般用静态动词（如官话中的累、饿、在、笨等等）表示，不需要系词连接。句子可以简单地由代词和这样的动词组成：例如“我饿”。然而通常，表达品质的动词由副词（“非常”、“不”、“相当”等）来修饰；当没有其他修饰时，它们通常跟在“很”（意思是“非常”）的后面，但在这种用法中通常没有具体的意思。参见汉语语法。
只有名词作为补语的句子（例如“这是我的妹妹”）使用系动词“是”。这经常用到：例如，不常说“是中国的”，常用的表达是“是中国人”（我是中国人，「I am a Chinese person」）。这里的“是”是动词。另一种可能性是补语只是一个名词修饰语（以“的”字结尾），名词省略：我的汽车是红色的（即“我的汽车是红色的汽车”）。
汉朝以前，“是”用作指示代词，意思是“这”（这种用法在一些成语和谚语以及日语中保留下来）。一些语言学界认为“是”之所以发展成为系动词是因为其在句子的主语之后，经常作为重复主语出现（在文言文中，我们可以说“乔治·W·布什，"是"美国之总统”，直译是“乔治·W·布什这个美国总统”，也就表明了“乔治·W·布什"是"美国总统”）。 “是”这个字是由日和正两个字结合而成的。
现代汉语中“是”可以和“的”字连用，表示应承或同意，例如问：你的汽车是不是红色的？
答：是的。意思是“就是红色的”，或者回答“不是”，意思是“不是红色的”。（当然也可以回答“对”或“不对”。）“是”还有种用法是“是……的”结构，用来强调句子的特定成分；参见汉语语法→分裂句。
在泉漳闽语中“是（"sī"）”用作系词，与吴语中的“是”相同。粤语用“系 （/hɐi˨/）”而不用“是”；同样，客家话也用“系（"he55"）”。