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In linguistics, a copula (plural: copulas or copulae; abbreviated ) is a word or phrase that links the subject of a sentence to a subject complement, such as the word ''is'' in the sentence "The sky is blue" or the phrase ''was not being'' in the sentence "It was not being co-operative." The word ''copula'' derives from the Latin noun for a "link" or "tie" that connects two different things.

A copula is often a verb or a verb-like word, though this is not universally the case. A verb that is a copula is sometimes called a copulative or copular verb. In English primary education grammar courses, a copula is often called a linking verb. In other languages, copulas show more resemblances to pronouns, as in Classical Chinese and Guarani, or may take the form of suffixes attached to a noun, as in Korean, Beja, and Inuit languages.

Most languages have one main copula, although some (like Spanish, Portuguese and Thai) have more than one, while others have none. In the case of English, this is the verb ''to be''. While the term ''copula'' is generally used to refer to such principal verbs, it may also be used for a wider group of verbs with similar potential functions (like ''become'', ''get'', ''feel'' and ''seem'' in English); alternatively, these might be distinguished as "semi-copulas" or "pseudo-copulas".

Grammatical function

The principal use of a copula is to link the subject of a clause to a subject complement. A copular verb is often considered to be part of the predicate, the remainder being called a predicative expression. A simple clause containing a copula is illustrated below:

The book is on the table.

In that sentence, the noun phrase ''the book'' is the subject, the verb ''is'' serves as the copula, and the prepositional phrase ''on the table'' is the predicative expression. The whole expression ''is on the table'' may (in some theories of grammar) be called a predicate or a verb phrase.

The predicative expression accompanying the copula, also known as the complement of the copula, may take any of several possible forms: it may be a noun or noun phrase, an adjective or adjective phrase, a prepositional phrase (as above) or an adverb or another adverbial phrase expressing time or location. Examples are given below (with the copula in bold and the predicative expression in italics):

The three components (subject, copula and predicative expression) do not necessarily appear in that order: their positioning depends on the rules for word order applicable to the language in question. In English (an SVO language), the ordering given above is the normal one, but certain variation is possible:
*In many questions and other clauses with subject–auxiliary inversion, the copula moves in front of the subject: ''Are you happy?''
*In inverse copular constructions (see below) the predicative expression precedes the copula, but the subject follows it: ''In the room were three men.''

It is also possible, in certain circumstances, for one (or even two) of the three components to be absent:
*In null-subject (pro-drop) languages, the subject may be omitted, as it may from other types of sentence. In Italian, means ‘I am tired’, literally ‘am tired’.
*In non-finite clauses in languages like English, the subject is often absent, as in the participial phrase ''being tired'' or the infinitive phrase ''to be tired''. The same applies to most imperative sentences like ''Be good!''
*For cases in which no copula appears, see below.
*Any of the three components may be omitted as a result of various general types of ellipsis. In particular, in English, the predicative expression may be elided in a construction similar to verb phrase ellipsis, as in short sentences like ''I am''; ''Are they?'' (where the predicative expression is understood from the previous context).

Inverse copular constructions, in which the positions of the predicative expression and the subject are reversed, are found in various languages. They have been the subject of much theoretical analysis, particularly in regard to the difficulty of maintaining, in the case of such sentences, the usual division into a subject noun phrase and a predicate verb phrase.

Another issue is verb agreement when both subject and predicative expression are noun phrases (and differ in number or person): in English, the copula typically agrees with the syntactical subject even if it is not logically (i.e. semantically) the subject, as in ''the cause of the riot is'' (not ''are'') ''these pictures of the wall''. Compare Italian ; notice the use of the plural to agree with plural "these photos" rather than with singular "the cause". In instances where an English syntactical subject comprises a prepositional object that is pluralized, however, the prepositional object agrees with the predicative expression, e.g. "What kind ''of birds are'' those?"

The definition and scope of the concept of a copula is not necessarily precise in any language. As noted above, though the concept of the copula in English is most strongly associated with the verb ''to be'', there are many other verbs that can be used in a copular sense as well.
* The boy became a man.
* The girl grew more excited as the holiday preparations intensified.
* The dog felt tired from the activity.

And more tenuously
* The milk turned sour.
* The food smells good.
* You seem upset.

Meanings

Predicates formed using a copula may express identity: that the two noun phrases (subject and complement) have the same referent or express an identical concept:

They may also express membership of a class or a subset relationship:

Similarly they may express some property, relation or position, permanent or temporary:

Other special uses of copular verbs are described in some of the following sections.

Essence vs. state

Some languages use different copulas, or different syntax, to denote a permanent, essential characteristic of something versus a temporary state. For examples, see the sections on the Romance languages, Slavic languages and Irish.

Forms

In many languages the principal copula is a verb, like English ''(to) be'', German , Mixtec , Touareg ''emous'', etc. It may inflect for grammatical categories like tense, aspect and mood, like other verbs in the language. Being a very commonly used verb, it is likely that the copula has irregular inflected forms; in English, the verb ''be'' has a number of highly irregular (suppletive) forms and has more different inflected forms than any other English verb (''am'', ''is'', ''are'', ''was'', ''were'', etc.; see English verbs for details).

Other copulas show more resemblances to pronouns. That is the case for Classical Chinese and Guarani, for instance. In highly synthetic languages, copulas are often suffixes, attached to a noun, but they may still behave otherwise like ordinary verbs: in Inuit languages.

In some other languages, like Beja and Ket, the copula takes the form of suffixes that attach to a noun but are distinct from the person agreement markers used on predicative verbs. This phenomenon is known as ''nonverbal person agreement'' (or ''nonverbal subject agreement''), and the relevant markers are always established as deriving from cliticized independent pronouns.

For cases in which the copula is omitted or takes zero form, see below.

Additional uses of copular verbs

A copular verb may also have other uses supplementary to or distinct from its uses as a copula.

As auxiliary verbs

The English verb ''to be'' is also used as an auxiliary verb, especially for expressing passive voice (together with the past participle) or expressing progressive aspect (together with the present participle):

Other languages' copulas have additional uses as auxiliaries. For example, French can be used to express passive voice similarly to English ''be''; both French and German are used to express the perfect forms of certain verbs (formerly English ''be'' was also):

The auxiliary functions of these verbs derived from their copular function, and could be interpreted as special cases of the copular function (with the verbal forms it precedes being considered adjectival).

Another auxiliary usage in English is (together with the ''to''-infinitive) to denote an obligatory action or expected occurrence: "I am to serve you;" "The manager is to resign." This can be put also into past tense: "We were to leave at 9." For forms like "if I was/were to come," see English conditional sentences. (Note that, by certain criteria, the English copula ''be'' may always be considered an auxiliary verb; see Diagnostics for identifying auxiliary verbs in English.)

Existential usage

The English ''to be'' and its equivalents in certain other languages also have a non-copular use as an existential verb, meaning "to exist." This use is illustrated in the following sentences: ''I want only to be, and that is enough''; '' I think therefore I am''; '' To be or not to be, that is the question.'' In these cases, the verb itself expresses a predicate (that of existence), rather than linking to a predicative expression as it does when used as a copula. In ontology it is sometimes suggested that the "is" of existence is reducible to the "is" of property attribution or class membership; to be, Aristotle held, is to be ''something''. However, Abelard in his ''Dialectica'' made a ''reductio ad absurdum'' argument against the idea that the copula can express existence.

Similar examples can be found in many other languages; for example, the French and Latin equivalents of ''I think therefore I am'' are and , where and are the equivalents of English "am," normally used as copulas. However, other languages prefer a different verb for existential use, as in the Spanish version (where the verb "to exist" is used rather than the copula or ‘to be’).

Another type of existential usage is in clauses of the ''there is…'' or ''there are…'' type. Languages differ in the way they express such meanings; some of them use the copular verb, possibly with an expletive pronoun like the English ''there'', while other languages use different verbs and constructions, like the French (which uses parts of the verb ‘to have,’ not the copula) or the Swedish (the passive voice of the verb for "to find"). For details, see existential clause.

Relying on a unified theory of copular sentences, it has been proposed that the English ''there''-sentences are subtypes of inverse copular constructions.

Zero copula

In some languages, copula omission occurs within a particular grammatical context. For example, speakers of Russian, Indonesian, Turkish, Hungarian, Arabic, Hebrew, Geʽez and Quechuan languages consistently drop the copula in present tense: Russian: , ‘I (am a) person;’ Indonesian: ‘I (am) a human;’ Turkish: ‘s/he (is a) human;’ Hungarian: ‘s/he (is) a human;’ Arabic: أنا إنسان, ‘I (am a) human;’ Hebrew: אני אדם, ''ʔani ʔadam'' "I (am a) human;" Geʽez: አነ ብእሲ/ብእሲ አነ ''ʔana bəʔəsi'' / ''bəʔəsi ʔana'' "I (am a) man" / "(a) man I (am)"; Southern Quechua: ''payqa runam'' "s/he (is) a human." The usage is known generically as the zero copula. Note that in other tenses (sometimes in forms other than third person singular), the copula usually reappears.

Some languages drop the copula in poetic or aphorismic contexts. Examples in English include
* ''The more, the better.''
* ''Out of many, one.''
* ''True that.''
Such poetic copula dropping is more pronounced in some languages other than English, like the Romance languages.

In informal speech of English, the copula may also be dropped in general sentences, as in "She a nurse." It is a feature of African-American Vernacular English, but is also used by a variety of other English speakers in informal contexts. An example is the sentence "I saw twelve men, each a soldier."

Examples in specific languages

In Ancient Greek, when an adjective precedes a noun with an article, the copula is understood: , "the house is large," can be written , "large the house (is)."

In Quechua (Southern Quechua used for the examples), zero copula is restricted to present tense in third person singular (''kan''): ''Payqa runam''  — "(s)he is a human;" but: ''(paykuna) runakunam kanku'' "(they) are human."ap

In Māori, the zero copula can be used in predicative expressions and with continuous verbs (many of which take a copulative verb in many Indo-European languages) — ''He nui te whare'', literally "a big the house," "the house (is) big;" ''I te tēpu te pukapuka'', literally "at (past locative particle) the table the book," "the book (was) on the table;" ''Nō Ingarangi ia'', literally "from England (s)he," "(s)he (is) from England," ''Kei te kai au'', literally "at the (act of) eating I," "I (am) eating."

Alternatively, in many cases, the particle ''ko'' can be used as a copulative (though not all instances of ''ko'' are used as thus, like all other Maori particles, ''ko'' has multiple purposes): ''Ko nui te whare'' "The house is big;" ''Ko te pukapuka kei te tēpu'' "It is the book (that is) on the table;" ''Ko au kei te kai'' "It is me eating."

However, when expressing identity or class membership, ''ko'' must be used: ''Ko tēnei tāku pukapuka'' "This is my book;" ''Ko Ōtautahi he tāone i Te Waipounamu'' "Christchurch is a city in the South Island (of New Zealand);" ''Ko koe tōku hoa'' "You are my friend."

When expressing identity, ''ko'' can be placed on either object in the clause without changing the meaning (''ko tēnei tāku pukapuka'' is the same as ''ko tāku pukapuka tēnei'') but not on both (''ko tēnei ko tāku pukapuka'' would be equivalent to saying "it is this, it is my book" in English).

In Hungarian, zero copula is restricted to present tense in third person singular and plural: ''Ő ember''/''Ők emberek'' — "s/he is a human"/"they are humans;" but: ''(én) ember vagyok'' "I am a human," ''(te) ember vagy'' "you are a human," ''mi emberek vagyunk'' "we are humans," ''(ti) emberek vagytok'' "you (all) are humans." The copula also reappears for stating locations: ''az emberek a házban vannak'', "the people are in the house," and for stating time: ''hat óra van'', "it is six o'clock." However, the copula may be omitted in colloquial language: ''hat óra (van)'', "it is six o'clock."

Hungarian uses copula ''lenni'' for expressing location: ''Itt van Róbert'' "Bob is here," but it is omitted in the third person present tense for attribution or identity statements: ''Róbert öreg'' "Bob is old;" ''ők éhesek'' "They are hungry;" ''Kati nyelvtudós'' "Cathy is a linguist" (but ''Róbert öreg volt'' "Bob was old," ''éhesek voltak'' "They were hungry," ''Kati nyelvtudós volt'' "Cathy was a linguist).

In Turkish, both the third person singular and the third person plural copulas are omittable. ''Ali burada'' and ''Ali buradadır'' both mean "Ali is here," and ''Onlar aç'' and ''Onlar açlar'' both mean "They are hungry." Both of the sentences are acceptable and grammatically correct, but sentences with the copula are more formal.

The Turkish first person singular copula suffix is omitted when introducing oneself. ''Bora ben'' (I am Bora) is grammatically correct, but "Bora benim" (same sentence with the copula) is not for an introduction (but is grammatically correct in other cases).

Further restrictions may apply before omission is permitted. For example, in the Irish language, ''is'', the present tense of the copula, may be omitted when the predicate is a noun. ''Ba'', the past/conditional, cannot be deleted. If the present copula is omitted, the pronoun (e.g., ''é, í, iad'') preceding the noun is omitted as well.

Additional copulas

Sometimes, the term ''copula'' is taken to include not only a language's equivalent(s) to the verb ''be'' but also other verbs or forms that serve to link a subject to a predicative expression (while adding semantic content of their own). For example, English verbs like ''become'', ''get'', ''feel'', ''look'', ''taste'', ''smell'', and ''seem'' can have this function, as in the following sentences (the predicative expression, the complement of the verb, is in italics):

(This usage should be distinguished from the use of some of these verbs as "action" verbs, as in ''They look at the wall'', in which ''look'' denotes an action and cannot be replaced by the basic copula ''are''.)

Some verbs have rarer, secondary uses as copular verbs, like the verb ''fall'' in sentences like ''The zebra fell victim to the lion.''

These extra copulas are sometimes called "semi-copulas" or "pseudo-copulas." For a list of common verbs of this type in English, see List of English copulae.

In particular languages

Indo-European

In Indo-European languages, the words meaning ''to be'' are sometimes similar to each other. Due to the high frequency of their use, their inflection retains a considerable degree of similarity in some cases. Thus, for example, the English form ''is'' is a cognate of German ''ist'', Latin ''est'', Persian ''ast'' and Russian ''jest''', even though the Germanic, Italic, Iranian 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-'').

English

The English copular verb ''be'' has eight forms (more than any other English verb): ''be'', ''am'', ''is'', ''are'', ''being'', ''was'', ''were'', ''been''. Additional archaic forms include ''art'', ''wast'', ''wert'', and occasionally ''beest'' (as a subjunctive). For more details see English verbs. For the etymology of the various forms, see Indo-European copula.

The main uses of the copula in English are described in the above sections. The possibility of copula omission is mentioned under .

A particular construction found in English (particularly in speech) is the use of two successive copulas when only one appears necessary, as in ''My point is, is that...''. The acceptability of this construction is a disputed matter in English prescriptive grammar.

The simple English copula "be" may on occasion be substituted by other verbs with near identical meanings.

Persian

In Persian, the verb ''to be'' can either take the form of ''ast'' (cognate to English ''is'') or ''budan'' (cognate to ''be'').

:

Hindustani

In Hindustani (Hindi and Urdu