In linguistics, grammatical number is a grammatical category of nouns, pronouns, and adjective and verb agreement that expresses count distinctions (such as "one", "two", or "three or more"). In many languages, including English, the number categories are singular and plural. Some languages also have a dual, trial, and paucal number or other arrangements.
The word "number" is also used in linguistics to describe the distinction between certain grammatical aspects that indicate the number of times an event occurs, such as the semelfactive aspect, the iterative aspect, etc. For that use of the term, see "Grammatical aspect".
Most languages of the world have formal means to express differences of number. One widespread distinction, found in English and many other languages, involves a simple two-way number contrast between singular and plural (car/cars, child/children, etc.). Discussion of other more elaborate systems of number appears below.
Grammatical number is a morphological category characterized by the expression of quantity through inflection or agreement. As an example, consider the English sentences below:
The number of apples is marked on the noun—"apple" singular number (one item) vs. "apples" plural number (more than one item)—on the demonstrative, "that/those", and on the verb, "is/are". In the second sentence, all this information is redundant, since quantity is already indicated by the numeral "two".
A language has grammatical number when its nouns are subdivided into morphological classes according to the quantity they express, such that:
This is partly the case in English: every noun is either singular or plural (a few forms, such as "fish", can be either, according to context), and at least some modifiers of nouns—namely the demonstratives, the personal pronouns, the articles, and verbs—are inflected to agree with the number of the nouns to which they refer: "this car" and "these cars" are correct, while "*this cars" or "*these car" are ungrammatical and, therefore, incorrect. However adjectives are not inflected, and most verb forms do not distinguish between singular and plural. Only count nouns can be freely used in the singular and in the plural. Mass nouns, like "milk", "silverware", and "wisdom", are normally used in only the singular form. (In some cases, a normally mass noun X may be used as a count noun to collect several distinct kinds of X into an enumerable group; for example, a cheesemaker might speak of goat, sheep, and cow milk as milks.) Many languages distinguish between count nouns and mass nouns.
Not all languages have number as a grammatical category. In those that do not, quantity must be expressed either directly, with numerals, or indirectly, through optional quantifiers. However, many of these languages compensate for the lack of grammatical number with an extensive system of measure words.
There is a hierarchy among number categories: no language distinguishes a trial (indicating the number 3) unless it has a dual, and no language has a dual without a plural.
Obligatory plural marking of all nouns is found throughout western and northern Eurasia and in most parts of Africa. The rest of the world presents a heterogeneous picture. Optional plural marking is particularly common in Southeast and East Asia and Australia, and complete lack of plural marking is particularly found in New Guinea and Australia. In addition to the areal correlations, there also seems to be at least one correlation with morphological typology: isolating languages appear to favor no or non-obligatory plural marking. This can be seen particularly in Africa, where optionality or absence of plural marking is found particularly in the isolating languages of West Africa.
English is typical of most world languages, in distinguishing only between singular and plural number. The plural form of a noun is usually created by adding the suffix -(e)s. The pronouns have irregular plurals, as in "I" versus "we", because they are ancient and frequently used words going back to when English had a well developed system of declension. English verbs distinguish singular from plural number in the third person present tense ("He goes" versus "They go"). English treats zero with the plural number. Old English did contain dual grammatical numbers.
The Finnish language has a plural form of almost every noun case (except the comitative, which is formally only plural).
However, when a number is used, or a word signifying a number (monta- many), the singular version of the partitive case is used.
and where no specific number is mentioned, the plural version of the partitive case is used
and in the possessive (genitive)
In modern Romance languages, nouns, adjectives and articles are declined according to number (singular or plural only). Verbs are conjugated for number as well as person. French treats zero as using the singular number, not the plural.
In its written form, French declines nouns for number (singular or plural). In speech, however, the majority of nouns (and adjectives) are not declined for number. The typical plural suffix, -s or -es, is silent, no longer indicating a change in pronunciation. Spoken number marking on the noun appears when liaison occurs.
Normally, the article or determiner is the primary indicator of number.
In Modern Hebrew, a Semitic language, most nouns have only singular and plural forms, such as ספר /ˈsɛfɛʁ/ "book" and ספרים /sfaˈʁim/ "books", but some have distinct dual forms using a distinct dual suffix (largely nouns pertaining to numbers or time, such as אלפיים /alˈpajim/ "two thousand" and שבועיים /ʃvuˈajim/ "two weeks"), some use this dual suffix for their regular plurals (largely body parts that tend to come in pairs, such as עיניים /eɪˈnajim/ "eyes", as well as some that do not, such as שיניים /ʃiˈnajim/ "teeth"), and some are inherently dual (such as מכנסיים /mɪxnaˈsajim/ "pants" and אופניים /ofaˈnajim/ "bicycle"). Adjectives, verbs, and pronouns agree with their subjects' or antecedents' numbers, but only have a two-way distinction between singular and plural; dual nouns entail plural adjectives, verbs, and pronouns.
Modern Russian has a singular vs plural number system, but the declension of noun phrases containing numeral expressions follows complex rules. For example, "У меня есть одна книга/три книги/пять книг" ("I have one book-nom. sing./three book-nom. plur./five book-gen. plur."). See Dual number: Slavic languages for a discussion of number phrases in Russian and other Slavic languages.
The numeral "one" also has a plural form, used with pluralia tantum: одни джинсы/одни часы "one pair of jeans, one clock". The same form is used with countable nouns in meaning "only": Кругом одни идиоты "There are only idiots around".
Swedish inflects nouns in singular and plural. The plural of the noun is usually obtained by adding a suffix, according to the noun's declension. The suffixes are as follows: -or in the 1st declension (e.g. flicka - flickor), -ar in the 2nd (e.g. bil - bilar), -er in the 3rd (e.g. katt - katter), -n in the 4th (e.g. äpple - äpplen) and no inflectional suffix is added for the nouns in the 5th declension (e.g. bord - bord). Verbs in Swedish do not distinguish singular from plural number.
Tokelau is an Austronesian Island consisting of three atolls. The Tokelauan language has three types of personal pronouns - 1st person, 2nd person inclusive, 2nd person exclusive, and 3rd person exclusive. The language has unique ways to address multiple people in one conversation. For example, the generic greeting for ‘Hello’ is Tālofa or Mālō. To greet one person, ‘greetings to you’ would be the same as the common greeting. To address two people, Tālofa nī/Mālō nī Fakatālofa atu kia te koulua; koulua is the dual third person term. To address three or more people, Fakatālofa atu kia te koutou; koutou is the plural third person term.
Wuvulu is an Austronesian Island located in the Manus Province of Papua New Guinea. The languages numbering system is multiplicative construction, where each number is based on multiplying pre-existing numbers smaller than five. Wuvulu is most similar to most Proto-Oceanic languages, and their numbering system is representative of some systems found in the Marshall Islands. For examples, the number two in Wuvulu is roa and the number four in both Proto-Oceanic language and Wuvulu is fa. Therefore, the number eight in Wuvulu the construction of two and four, resulting in fainaroa, translating into "four multiply two". Moreover, the Wuvulu language has different numerical systems for animate objects and inanimates objects. When referencing an inanimate object, the number seven is oloompalo; however, if it is an animate object, the word changes to oloromea. The structure of a noun phrase looks like " NP=(ART/DEMONSTRATIVE+)(NUMBER/QUANTIFIER+)(PREMODIFIERS+)NOUN(+MODIFER.) As we can see, the number or quantifier appears in the middle of the noun phrase. 
ʔi=na-tafi-ʔa oloroa wa
3SG=REAL-carve-TR six canoe
He carved six canoes.
The Mortlockese language of the Mortlock Islands uses a base 10 counting system. Pronouns, nouns and demonstratives are used exclusively in the singular and plural forms through the use of classifiers, suffixes and prefixes.  There are no other dual or trial grammatical forms in the Mortlockese language.  Different forms that can be used in the language include first person singular and plural words, second person singular words like “umwi,” second person plural words like “aumi” used to refer to an outside group, and third person plural words. 
In most languages with grammatical number, nouns, and sometimes other parts of speech, have two forms, the singular, for one instance of a concept, and the plural, for more than one instance. Usually, the singular is the unmarked form of a word, and the plural is obtained by inflecting the singular. This is the case in English: car/cars, box/boxes, man/men. There may be exceptional nouns whose plural is identical to the singular: one sheep/two sheep.
Some languages differentiate between an unmarked form, the collective, which is indifferent in respect to number, and a marked form for single entities, called the singulative in this context. For example, in Welsh, moch ("pigs") is a basic form, whereas a suffix is added to form mochyn ("pig"). It is the collective form which is more basic, and it is used as an adjectival modifier, e.g. cig moch ("pig meat", "pork"). The collective form is therefore similar in many respects to an English mass noun like "rice", which in fact refers to a collection of items which are logically countable. However, English has no productive process of forming singulative nouns (just phrases such as "a grain of rice"). Therefore, English cannot be said to have a singulative number.
In other languages, singulatives can be regularly formed from collective nouns; e.g. Standard Arabic حجر ḥajar "stone" → حجرة ḥajara "(individual) stone", بقر baqar "cattle" → بقرة baqara "(single) cow". In Russian, the suffix for forming singulative form is -ин- -in-; e.g. град grad "hail" → градина gradina "hailstone", лёд lyod "ice" → льдина l'dina "block of ice". In both Russian and Arabic, the singulative form always takes on the feminine gender. In Dutch, singulative forms of collective nouns are occasionally made by diminutives: snoep "sweets, candy" → snoepje "sweet, piece of candy". These singulatives can be pluralised like most other nouns: snoepjes "several sweets, pieces of candy".
The distinction between a "singular" number (one) and a "plural" number (more than one) found in English is not the only possible classification. Another one is "singular" (one), "dual" (two) and "plural" (more than two). Dual number existed in Proto-Indo-European, persisted in many ancient Indo-European languages that descended from it—Sanskrit, Ancient Greek, Gothic, Old Norse, and Old English for example—and can still be found in a few modern Indo-European languages such as Slovene. Many more modern Indo-European languages show residual traces of the dual, as in the English distinctions both vs. all, either vs. any, neither vs. none, and so on. (Note, however, that Norwegian både, for example, though cognate with English both, can be used with more than two things, as in X sparer både tid, penger, og arbeid, literally "X saves both time, money, and labour".)
Many Semitic languages also have dual number. For instance, in Arabic all nouns can have singular, plural, or dual forms. For non-broken plurals, masculine plural nouns end with ون -ūn and feminine plural nouns end with ات -āt, whilst ان -ān, is added to the end of a noun to indicate that it is dual (even among nouns that have broken plurals).
The trial number is a grammatical number referring to 'three items', in contrast to 'singular' (one item), 'dual' (two items), and 'plural' (four or more items). Several Austronesian languages such as Tolomako, Lihir, and Manam; the Kiwaian languages; and the Austronesian-influenced creole languages Bislama and Tok Pisin have the trial number in their pronouns. No language is known with trial number in its nouns.
The quadral number, if it existed, would denote four items together, as trial does three. No known natural language has it, nor is there any proof that any natural language ever did. It was once thought to exist in the pronoun systems of Marshallese, spoken in the Marshall Islands in the Pacific Ocean, and in Sursurunga, in Tangga, and in several other Austronesian languages. While not all of these languages are adequately attested, it turns out that Sursurunga instead has both a "lesser paucal" (labeled "trial", but in fact referring to small groups, with typically three or four members) and a "greater paucal" (misnamed the "quadral", as it has a minimum of four, e.g. a pair of dyadic kin terms)—the distinction is along the lines of "a few" vs. "several";—and that what Marshallese actually has is a trial and a paucal. None of them has a "quadral"; in at least two cases the field workers who originally suggested they did have a "quadral" were also the first to publish a peer-reviewed article contradicting that suggestion.
Paucal number, for a few (as opposed to many) instances of the referent (e.g. in Hopi, Warlpiri, some Oceanic languages, Motuna, Serbo-Croatian, and in Arabic for some nouns). Paucal number has also been documented in some Cushitic languages of Ethiopia, including Baiso, which marks singular, paucal, plural. When paucal number is used in Arabic, it generally refers to ten or fewer instances.
Of the Indo-European languages, Northern Kurdish or Kurmanji is one of the few known languages with paucal number. In Russian, the genitive singular is also applied to three or four items (2, 3, 4 ка́мня – stones, gen. sg.; but 5...20 камне́й - stones, gen. pl.), making it effectively paucal (cf. э́тот ка́мень - this stone, nom. sg.; э́ти ка́мни - these stones, nom. pl.). Polish functions similarly: 'one dog' is 'jeden pies', while (2, 3, 4 psy - dogs, pl.; but 5+ psów - dogs, gen. pl.).
Distributive plural number, for many instances viewed as independent individuals (for example, in Navajo).
Synthetic languages typically distinguish grammatical number by inflection. (Analytic languages, such as Chinese, often do not mark grammatical number.) Some languages have no marker for the plural in certain cases, e. g. Swedish hus – "house, houses" (but huset – "the house", husen – "the houses"). In most languages, the singular is formally unmarked, whereas the plural is marked in some way. Other languages, most notably the Bantu languages, mark both the singular and the plural, for instance Swahili (see example below). The third logical possibility, rarely found in languages, is an unmarked plural contrasting with marked singular. Below are some examples of number affixes for nouns (where the inflecting morphemes are underlined):
|Paul is teaching the cowboy.||Paul idilohí yiłch’ígó’aah.|
|Paul is teaching the cowboys.||Paul idilohí yiłch’ídagó’aah.|
In the English sentence above, the plural suffix -s is added to the noun cowboy. In the equivalent in Western Apache, a head-marking language, a plural infix da- is added to the verb yiłch’ígó’aah "he is teaching him", resulting in yiłch’ídagó’aah "he is teaching them" while noun idilohí "cowboy" is unmarked for number.
Spanish marks nouns, pronouns, articles and adjectives.
Plurality is sometimes marked by a specialized number particle (or number word). This is frequent in Australian and Austronesian languages. An example from Tagalog is the word mga [mɐˈŋa]: compare bahay "house" with mga bahay "houses". In Kapampangan, certain nouns optionally denote plurality by secondary stress: ing laláki "man" and ing babái "woman" become ding láláki "men" and ding bábái "women".
In Sanskrit and some other languages, number and case are fused category and there is concord for number between a noun and its predicator. Some languages however (for example, Assamese) lack this feature.
Languages that show number inflection for a large enough corpus of nouns or allow them to combine directly with singular and plural numerals can be described as non-classifier languages. On the other hand, there are languages that obligatorily require a counter word or the so-called classifier for all nouns. For example, the category of number in Assamese is fused with the category of classifier, which always carries a definite/indefinite reading. The singularity or plurality of the noun is determined by the addition of the classifier suffix either to the noun or to the numeral. Number system in Assamese is either realized as numeral or as nominal inflection, but not both. Numerals [ek] 'one' and [dui] 'two', can be realized as both free morpheme and clitics. When used with classifiers, these two numerals are cliticised to the classifiers.
Pingelapese is a Micronesian language spoken on the Pingelap atoll and on two of the eastern Caroline Islands, called the high island of Pohnpei. In Pingelapese, the meaning, use, or shape of an object can be expressed through the use of numerical classifiers. These classifiers combine and noun and a number that together can give more details about the object. There are at least five sets of numerical classifiers in Pingelapese. Each classifier has a numeral part and a classifier part that corresponds to the noun it is describing. The classifier follows the noun in a phrase. There is a separate set of numerical classifiers that is used when the object is not specified. Examples of this is the names of the days of the week.
In many languages, such as English, number is obligatorily expressed in every grammatical context. Some limit number expression to certain classes of nouns, such as animates or referentially prominent nouns (as with proximate forms in most Algonquian languages, opposed to referentially less prominent obviative forms). In others, such as Chinese and Japanese, number marking is not consistently applied to most nouns unless a distinction is needed or already present.
A very common situation is for plural number to not be marked if there is any other overt indication of number, as for example in Hungarian: virág "flower"; virágok "flowers"; hat virág "six flowers".
Many languages, such as Chinese, Indonesian, Japanese and Malay, have optional number marking. In such cases, an unmarked noun is neither singular nor plural, but rather ambiguous as to number. This is called transnumeral or sometimes general number, abbreviated TRN. Many such languages have optional number marking, which tends to be used for definite and highly animate referents, most notably first-person pronouns.
The languages of the Tanoan family have three numbers – singular, dual, and plural – and exhibit an unusual system of marking number, called inverse number (or number toggling). In this scheme, every countable noun has what might be called its "inherent" or "expected" numbers, and is unmarked for these. When a noun appears in an "inverse" (atypical) number, it is inflected to mark this. For example, in Jemez, where nouns take the ending -sh to denote an inverse number, there are four noun classes which inflect for number as follows:
|II||some inanimate nouns||-sh||-sh||-|
|III||other inanimate nouns||-||-sh||-|
|IV||mass (non-countable) nouns||(n/a)||(n/a)||(n/a)|
As can be seen, class-I nouns are inherently singular, class-II nouns are inherently plural, class-III nouns are inherently singular or plural. Class-IV nouns cannot be counted and are never marked with -sh.* 
A similar system is seen in Kiowa (Kiowa is distantly related to Tanoan languages like Jemez):
(See also Taos language: Number inflection for a description of inverse number suffixes in another Tanoan language.)
In many languages, verbs are conjugated according to number. Using French as an example, one says je vois (I see), but nous voyons (we see). The verb voir (to see) changes from vois in the first person singular to voyons in the plural. In everyday English, this often happens in the third person (she sees, they see), but not in other grammatical persons, except with the verb to be.
Adjectives often agree with the number of the noun they modify. For example, in French, one says un grand arbre [œ̃ ɡʁɑ̃t aʁbʁ] "a tall tree", but deux grands arbres [dø ɡʁɑ̃ zaʁbʁ] "two tall trees". The singular adjective grand becomes grands in the plural, unlike English "tall", which remains unchanged.
Other determiners may agree with number. In English, the demonstratives "this", "that" change to "these", "those" in the plural, and the indefinite article "a", "an" is either omitted or changes to "some". In French and German, the definite articles have gender distinctions in the singular but not the plural. In Italian, Spanish and Portuguese, both definite and indefinite articles are inflected for gender and number, e.g. Portuguese o, a "the" (singular, masc./fem.), os, as "the" (plural, masc./fem.); um, uma "a(n)" (singular, masc./fem.), uns, umas "some" (plural, masc./fem.), dois, duas "two" (plural, masc./fem.),
Sometimes, grammatical number will not represent the actual quantity. For example, in Ancient Greek neuter plurals took a singular verb. The plural form of a pronoun may also be applied to a single individual as a sign of importance, respect or generality, as in the pluralis majestatis, the T-V distinction, and the generic "you", found in many languages, or, in English, when using the singular "they" for gender-neutrality.
In Arabic, the plural of a non-human noun (one that refers to an animal or to an inanimate entity regardless of whether the noun is grammatically masculine or feminine in the singular) is treated as feminine singular—this is called the inanimate plural. For example:
A collective noun is a word that designates a group of objects or beings regarded as a whole, such as "flock", "team", or "corporation". Although many languages treat collective nouns as singular, in others they may be interpreted as plural. In British English, phrases such as the committee are meeting are common (the so-called agreement in sensu "in meaning"; with the meaning of a noun, rather than with its form, see constructio ad sensum). The use of this type of construction varies with dialect and level of formality.
In some cases, the number marking on a verb with a collective subject may express the degree of collectivity of action:
All languages are able to specify the quantity of referents. They may do so by lexical means with words such as English a few, some, one, two, five hundred. However, not every language has a grammatical category of number. Grammatical number is expressed by morphological or syntactic means. That is, it is indicated by certain grammatical elements, such as through affixes or number words. Grammatical number may be thought of as the indication of semantic number through grammar.
Languages that express quantity only by lexical means lack a grammatical category of number. For instance, in Khmer, neither nouns nor verbs carry any grammatical information concerning number: such information can only be conveyed by lexical items such as khlah 'some', pii-bey 'a few', and so on.
Auxiliary languages often have fairly simple systems of grammatical number. In one of the most common schemes (found, for example, in Interlingua and Ido), nouns and pronouns distinguish between singular and plural, but not other numbers, and adjectives and verbs do not display any number agreement. In Esperanto, however, adjectives must agree in both number and case with the nouns that they qualify.
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