An equative (or equational) sentence is a sentence where two entities are equated with each other. For example, the sentence Susan is our president, equates two entities "Susan" and "our president". In English, equatives are typically expressed using a copular verb such as "be", although this is not the only use of this verb. Equative sentences can be contrasted with predicative sentences where one entity is identified as a member of a set, such as Susan is a president. This view has been contrasted by Otto Jespersen in the first part of the XX century and by Giuseppe Longobardi and Andrea Moro in the second. In particular, Andrea Moro in 1988 proved that either demonstrative phrases (DP) must be non referential in the sense of Geach (1962) by exploiting arguments based on binding theory. The idea is that when a DP plays the role of predicate it enlarges its binding domain: for example, in John met his cook the pronoun can refer to the subject John but in John is his cook it cannot. The key-step was to admit that the DP following the copula can be referential whereas the one preceding must not, in other words the key-step was to admit that there can be inverse copular sentences, namely those where the subject, which is referential, follows the predicate. For a discussion starting from Moro's data see Heycock (2012). For a historical view of the development of the analysis of the copula, see Moro.

Different world languages approach equative sentences in different ways. The major difference between languages is whether or not they use a copular verb or a non-verbal element (e.g. demonstrative pronoun) to equate the two expressions.

History

Theories and debate

Debate on taxonomy

The taxonomy or classification of copular clauses proposed by Higgins is the starting point of much work on syntax and semantics of copular clauses. Higgins' taxonomy distinguishes between four types of copular clauses:

Predicational a. The hat is big. b. The hat/present/thing I bought for Harvey is big. c. What I bought for Harvey is big.

Specificational a. The director of Anatomy of Murder is Otto Preminger. b. The only director/person/one I met was Otto Preminger. c. Who I met was Otto Preminger.

Identificational a. That (woman) is Sylvia. b. That (stuff) is DDT.

Equative a. Sylvia Obernauer is HER. b. Cicero is Tully.

This taxonomy is based primarily on native speaker intuition, as well as on detailed observations of English copular sentences. The intuition about predicational clauses is that they predicate a property of the subject referent. The other three types of copular clauses do not involve predication. Equatives equate the referents of the two expressions on either side of the copular verb. Neither is a predicate of the other. Specificational clauses involve assigning a value to a variable: the subject expression sets up a variable and the post-copular expression provides the value for that variable. Identificational clauses typically involve a demonstrative subject and are used for teaching the names of people or of things. Many linguists are currently in disagreement regarding the taxonomy and status of equative clauses.

Reduction of taxonomy

Caroline Heycock Heycock, C. (2012). Specification, equation, and agreement in copular sentences. The Canadian Journal of Linguistics/La revue canadienne de linguistique, 57(2), 209-240. contributes to the discussion about whether specificational sentences are a special type of equatives or if they can be reduced to 'inverted predications': she argues that these sentences are a type of equative in which only one of the two noun phrases is a simple individual. Heycock claims that specificational sentences are an 'asymmetric' equation because the noun phrase that occurs in clause-initial position is interpreted as a more intentional subject than is the post-copular noun phrase.

Den Dikken Den Dikken, M. (2006). Relators and linkers: The syntax of predication, predicate inversion, and copulas (Vol. 47). MIT Press. states that the category of specificational sentences is more real and that it includes both categories (specificational and equative clauses).

Mikkelsen, on the other hand, maintains the distinction between specificational and equative clauses, but suggests that the identificational class be eliminated.

Moro Moro, A. (1997). The raising of predicates, Cambridge University Press, Cambridge, Uk. It proposes a unified theory of copular sentences reducing the types to two different arrangements of the same basic structure, including existential sentences; it also contains a historical appendix. Many theories stem from this work including, among others, Heycock's proposal.

Heller Heller, D. (2005). Identity and information: Semantic and pragmatic aspects of specificational sentences (Doctoral dissertation, Rutgers, The State University of New Jersey). goes further and gives a reduced taxonomy of two classes of clauses: predicational, which includes both identificational and predicational clauses, and equative, which involve equative and specificational clauses.

Debate on equatives

Linguists have also been arguing about the very existence of equative clauses as a separate class. There are languages that are claimed to lack equative constructions, e.g. Adger & Ramchand Adger, D. (2003). Predication and equation. Linguistic Inquiry, 34(3), 325-359. analyze Scottish Gaelic as a language without equatives. Some languages use more elaborate locutions, e.g. be the same person as in English to express the meaning of the sentence like Cicero is Tully. Geist Geist, L. (2007). Predication and equation in copular sentences: Russian vs. english. (pp. 79-105). Dordrecht: Springer Netherlands. claims that there are no monoclausal equatives in Russian. According to Geist, equation is mediated, syntactically and semantically, by a demonstrative pronoun. Mikkelsen argues that within English, outside special cases like Muhammad Ali is Cassius Clay, Mark Twain is Samuel Clemens, and Cicero is Tully, main clause equatives which involve two names are difficult to contextualize. However, equatives such as Sylvia Obernauer is HER, where one NP is a pronoun and the other is a name, are easier to contextualize: they are natural answers to Who is who? in a situation where individuals can be identified both by name or by sight, e.g. at the conference.

Halliday's semantic analysis of equatives

Halliday Halliday, M. A. K. (1968). Notes on transitivity and theme in English Part 3. Journal of linguistics, 4(02), 179-215. divides clauses into two categories: 'intensive', where the process is ascription (the assigning of an attribute) and the equative, which is treated as a type of effective clause with the process being syntactically one of action rather than ascription. The intensive clause, like Mary is/seems happy, Mary was/became a teacher, is a non-reversible, one-participant type with the verb being of the copulative class ('class o': be, becomes, seem, look, sound, get, turn, etc.); the equative, like 'John is the leader', is a reversible, two-participant type with the verb being of the equative sub-class (of 'class 2': be, equal, resemble, realize, represent, etc.).

The equative relates an 'identifier' with a 'thing to be identified', as in ('who is John?') // John is the leader //. This relates to the underlying WH-question, and either the identified or the identifier may come first in sequence. The equative has two interpretations, as decoding or as encoding: // John is the leader // as a decoding equative has the interpretation 'John realizes, has the function of the leader', with John as the variable and the leader as a value, and as an encoding equative has the interpretation' John is realized by, has the form of the leader', with John as value and the leader as variable. According to Halliday, all equative clauses are therefore ambiguous, for example: The noisiest ones are the freshmen. *Decoding: 'you notice those noisiest ones there? well they're freshmen' *Encoding: 'you want to know who makes the most noise? the freshmen do'

What they're selling might be sports clothes. *Decoding: 'what are those things they're selling? they might be sports clothes' *Encoding: 'what do they sell? they might sell sports clothes'

Copular equative constructions

Chinese Mandarin Chinese exhibits both DP-DP and DP-CP structures, and it is classified as having copular equative construction because there is overt copula. The copular verb 是 shì can be used in both of these structures.

DP = DP There is only one copular verb in Chinese, 是 shì, which is used as an equative verb. This verb is necessary when the complement of the sentence is a noun phrase.

In classical Chinese before the Han dynasty, the verb 是 served as a demonstrative pronoun meaning "this".Pulleyblank, Edwin G. (1995). Outline of Classical Chinese Grammar. Vancouver: UBC Press. . In modern Chinese, the complementizer 的 de is needed at the end of a noun phrase that changes the category to an adjectival phrase. Consider the following two sentences:

Whilst the two sentences aim to express the same meaning, only the second one is grammatical. The first cannot equate ’red' and 'boot(s)' without using the modifier 的 de.

DP = CP The example below illustrates how a DP can be equated with a CP clause by employing the copular verb 是 shì.

English

DP = DP Equative sentences resemble predicative sentences in that they have two noun phrases and the copular verb ‘to be’. However, the similarity is superficial. Compare the following two sentences: (4) Cicero is Tully. (5) Cicero is an orator and philosopher. Analysis of these sentences will show that there is a radical difference between the equative sentence and the predicational sentence in English. The predicational sentence in (5) ascribes the property to the referent noun phrase whereas the equative sentence basically says that the first and second noun phrase share the same referent. It is difficult to distinguish between a predicative and equative sentence in English as both use a similar construction and both require the copular verb ‘to be’. Unlike specificational sentences, truly equative sentences cannot be analyzed as syntactically inverted predications, because neither expression is functioning as a predicate. Note that even English examples like (4) have predicational interpretations, as in a context where Tully is a character in a play, or where Tully refers to the property of being named Tully, rather than referring to the actual referent.

Haitian Creole

DP = DP In Haitian Creole the equative clause pattern involves the equative copula sé which joins a subject noun phrase with a complement noun phrase that refers back to the subject.

A simple copula predicate consists of sé 'am/is/are' only. The negative marker pa and the TMA (tense-mood-aspect) markers can co-occur with the copula-type predicate, subject to certain rules (TMA markers: té 'past' or 'anterior', kay 'prospective' or 'irrealis', ka 'nonpunctual', sa 'abilitative'). One such rule is that té + sé → sété (or just té without sé). The combinations permitted in an equative clause are limited in natural speech: a maximum number of two tense, mood, aspect and copula morphemes can co-occur in a given clause.Escure, G., & Schwegler, A. (Eds.). (2004). Creoles, contact, and language change: Linguistic and social implications (Vol. 27). John Benjamins Publishing. Here are some examples of the equative clause type in Haitian Creole (predicates are in bold): (7) Ou sé jan mwen. 'You are my friend.' Ou té jan mwen. 'You were my friend.' Ou kay jan mwen. 'You will be my friend.' Ou pa té kay jan mwen. 'You wouldn't be my friend.' Ou sa jan mwen. 'You can be my friend.' Ou pa sa jan mwen. 'You cannot be my friend.' Non mwen sé Tjals. 'My name is Charles.' Tjals sété an Endyen. 'Charles was an Indian.'