Copula (linguistics)

In linguistics, a copula 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 cooperative." 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 have more than one, while others have none. 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 ; 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. In some theories of grammar, the whole expression is on the table may 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, 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 do not necessarily appear in that order: their positioning depends on the rules for word order applicable to the language in question. In English, 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 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 of the three components to be absent:
In null-subject languages, the subject may be omitted, as it may from other types of sentence. In Italian, sono stanco means, literally.
In non-finite clauses in languages such as 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 such as 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 such as I am; Are they?.
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 : in English, the copula typically agrees with the syntactical subject even if it is not logically the subject, as in the cause of the riot is these pictures of the wall. Compare Italian la causa della rivolta sono queste foto del muro; notice the use of the plural sono to agree with plural queste foto rather than with singular la causa. 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.
Other functions

A copular verb may also have other uses supplementary to or distinct from its uses as a copula. Some co-occurrences are common.

Auxiliary verb

The English verb to be is also used as an auxiliary verb, especially for expressing passive voice or expressing progressive aspect :
Other languages' copulas have additional uses as auxiliaries. For example, French être can be used to express passive voice similarly to English be; both French être and German sein are used to express the perfect forms of certain verbs:
In the same way, usage of English be in the present perfect, though archaic, is still commonly seen in old texts/translations:
The auxiliary functions of these verbs derived from their copular function, and could be interpreted as special cases of the copular function.
Another auxiliary usage in English is 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 such as "if I was/were to come", see English conditional sentences.

Existential verb

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, 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 Je pense, donc je suis and Cogito ergo sum, where suis and sum 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 Pienso, luego existo.
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 such as the English there, while other languages use different verbs and constructions, such as the French il y a or the Swedish finns. 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.

Meanings

Predicates formed using a copula may express identity: asserting that two noun phrases 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:
The use of copulas, especially in some of their functions, can evoke opposition. E-Prime eschews excessive copula-usage in the interests of clarity.
Deleuze and Guattari object to some implications of the verb "to be":

The tree imposes the verb 'to be,' but the fabric of the rhizome is the conjunction, 'and... and... and...' This conjunction carries enough force to shake and uproot the verb 'to be.' Where are you going? Where are you coming from? What are you heading for? These are totally useless questions. Making a clean slate, starting or beginning again from ground zero, seeking a beginning or a foundation all imply a false conception of voyage and movement.

Essence versus 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, such as English be, German sein, Mixtec kuu, Touareg emous, etc. It may inflect for grammatical categories such as 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 forms and has more different inflected forms than any other English verb.
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: -u- in Inuit languages.
In some other languages, such as 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, and the relevant markers are always established as deriving from cliticized independent pronouns.