Dual is a grammatical number that some languages use in addition to singular and plural. When a noun or pronoun appears in dual form, it is interpreted as referring to precisely two of the entities (objects or persons) identified by the noun or pronoun. Verbs can also have dual agreement forms in these languages.

Comparative characteristics

Many languages make a distinction between singular and plural: English, for example, distinguishes between man and men, or house and houses. In some languages, in addition to such singular and plural forms, there is also a dual form, which is used when exactly two people or things are meant. In many languages with dual forms, use of the dual is mandatory, and the plural is used only for groups greater than two. However, use of the dual is optional in some languages such as many modern Arabic dialects including Egyptian Arabic. In other languages such as Hebrew, the dual exists only for a few measure words and for words that naturally come in pairs and are not used in the plural except in rhetoric: eyes, ears, and so forth. In Slovene use of the dual is mandatory, but nouns which would not have a plural form have lost the original dual and adapted the etymological plural form as their dual.

Although relatively few languages have the dual number and most have no number or only singular and plural, using different words for groups of two and groups greater than two is not uncommon. English has words distinguishing dual vs. plural number, including: both/all, between/among, latter/last, either/any, and neither/none. Japanese, which has no grammatical number, also has words dochira (which of the two) and dore (which of the three or more), etc.

Use in modern languages

Among living languages, Modern Standard Arabic has a mandatory dual number, marked on nouns, verbs, adjectives and pronouns. (First-person dual forms, however, do not exist; compare this to the lack of third-person dual forms in the old Germanic languages.) Many of the spoken Arabic dialects have a dual marking for nouns (only), but its use is not mandatory. Likewise, Akkadian had a dual number, though its use was confined to standard phrases like "two hands", "two eyes", and "two arms".

The Inuktitut language uses dual forms; however, the related Greenlandic language does not (though it used to have them).

Austronesian languages, particularly Polynesian languages such as Hawaiian, Niuean and Tongan, possess a dual number for pronouns but not for nouns (indeed, they tend not to mark nouns for number at all). Other Austronesian languages, particularly those spoken in the Philippines, have a dual first-person pronoun; these languages include Ilokano (data), Tausug (kita), and Kapampangan (ikata). These forms mean we, but specifically you and I. This form once existed in Tagalog but has largely disappeared, save for certain rural dialects, since the middle of the 20th century.

The dual was a standard feature of the Proto-Uralic language, and lives on in Sami languages and Samoyedic languages, while other branches like Finnish, Estonian and Hungarian have lost it. Sami also features dual pronouns, expressing the concept of "we two here" as contrasted to "we". Nenets, a Samoyedic language, features a complete set of dual possessive suffixes for two systems, the number of possessors and the number of possessed objects (for example, "two houses of us two" expressed in one word).

The dual form is also used in several modern Indo-European languages, such as Scottish Gaelic, Slovene, Frisian and Sorbian (see below for details). The dual was a common feature of all early Slavic languages at the beginning of the second millennium.

Hebrew

Biblical and Mishnaic Hebrew

In Biblical, Mishnaic, and Medieval Hebrew, like Arabic and other Semitic Languages, all nouns can have singular, plural or dual forms, and there is still a debate whether there are vestiges of dual verbal forms and pronouns.^[1] However, in practice, most nouns use only singular and plural forms. Usually ?? is added to masculine words to make them plural for example ???/????? "book/books", whilst with feminine nouns the ? is replaced with ?? . For example ???/???? "cow/cows". An example of the dual form is ???/?????/???? "day/two days/[two or more] days". Some words occur so often in pairs that what is technically the dual form is in practice used for the general plural, such as ???/????? "eye/eyes", used even in a sentence like, "The spider has eight eyes." Sometimes, words can change meaning depending on whether the dual or plural form is used, for example; ?? could mean either "hand" or "handle", but ???? in the dual form always means hands, whilst ???? in the plural form means handles. Adjectives, verbs, and pronouns have only singular and plural, with the plural forms of these being used with dual nouns.

Modern Hebrew

In Modern Hebrew as used in Israel, there is also a dual number, but its use is very restricted. The dual form is usually used in expressions of time and number. These nouns have plurals as well, which are used for numbers higher than two, for example:

The dual is also used for some body parts, for instance:

??? (leg) ? ?????? (legs)

???? (ear) ? ??????? (ears)

??? (eye) ? ?????? (eyes)

?? (hand) ? ????? (hands)

In this case, even if there are more than two, the dual is still used, for instance ("a dog has four legs").

The dual in Indo-European languages

Linguists have concluded based on an analysis of living and dead languages that a dual can be reconstructed for the Proto-Indo-European language, which has been preserved in the earliest records of Indo-European languages. The best evidence for the dual can be found in Sanskrit and the Ancient Greek language used in Homeric texts, where its use was obligatory for all inflected categories including nouns, verbs, adjectives, and pronouns. The dual can also be found in Common Slavic and Proto-Germanic languages, as well as Old Irish and Avestan. Based on Sanskrit and the Slavic and Baltic languages, it can be established that the dual in Proto-Indo-European had only three distinct forms: a nominative-accusative-vocative, a dative-ablative-instrumental, and a genitive-locative form.

Although the dual can be reconstructed for Proto-Indo-European, it is currently rarely found in any of the daughter languages. The dual is still actively used in Scottish Gaelic dialects, Welsh, Breton, Sorbian, and Slovene. Remnants of the dual can be found in many of the remaining daughter languages, where certain forms of the noun are used with the number two (see below for examples).

The dual in Greek

The dual can be found in Ancient Greek Homeric texts such as the Iliad and the Odyssey, although its use is only sporadic, owing as much to artistic prerogatives as dictional and metrical requirements within the hexametric meter. There were only two distinct forms of the dual in Ancient Greek.

In classical Greek, the dual was all but lost, except in the Attic dialect of Athens, where it persisted until the fifth century B.C. Even in this case, its use depended on the author and certain stock expressions.

Koine Greek and Modern Greek do not have any remnants of the dual.

The dual in the Celtic languages

Reconstructed Common Celtic nominal and adjectival declensions contain distinct dual forms; pronouns and verbs do not. In Old Irish, nouns and the definite article still have dual forms, but only when accompanied by the numeral da "two". Traces of the dual remain in Middle Welsh, in nouns denoting pairs of body parts that incorporate the numeral two: e.g. deulin (from glin "knee"), dwyglust (from clust "ear").^[2]

In the modern languages, there are still significant remnants of dual number in Scottish Gaelic in nominal phrases containing the numeral dà (including the higher numerals 12, 22, etc.) As the following table shows, dà combines with a singular noun, which is lenited. Masculine nouns take no special inflection, but feminine nouns have a slenderized dual form, which is in fact identical to the dative singular.^[3]

Languages of the Brythonic branch do not have dual number. As mentioned above for Middle Welsh, some nouns can be said to have dual forms, prefixed with a form of the numeral "two" (Breton daou-/div-, Welsh dau-/deu-/dwy-, Cornish dew-/diw-). This process is not fully productive, however, and the prefixed forms are semantically restricted. For example, Breton daouarn (< dorn "hand") can only refer to one person's pair of hands, not any two hands from two different people. Welsh deufis must refer to a period of two consecutive months, whereas dau fis can be any two months.^[4]

The dual in the Germanic languages

The dual was present in all the early Germanic languages, as well as in Proto-Germanic.

Gothic had markings for the first and second person for both the verbs and pronouns, for example wit "we two" as compared to weis "we, more than two". Old English, Old Norse and other old Germanic languages had dual marking only on first and second person pronouns.

The dual has disappeared as a productive form in all the living languages, with loss of the dual occurring in North Frisian dialects only quite recently^[5]. In Austro-Bavarian, the old dual pronouns have replaced the standard plural pronouns, for example, accusative enk, you plural. A similar development in the pronoun system can be seen in Icelandic and Faroese. Another remnant of the dual can be found in the use of the pronoun begge ("both") in the Scandinavian languages of Norwegian, Danish, and Swedish and báðir/báðar/bæði in Faroese. In these languages, in order to state "all + number", the constructions are begge to/báðir tveir/báðar tvær/bæði tvey ("all two") but alle tre/allir tríggir/allar tríggjar/øll trý ("all three"), while the form *alle to is unattested.

Though Modern English does not have dual number, it has some similar phenomena outside its core morphology. One involves the difference between the comparative and superlative forms of adjectives. Comparatives agree with sets of two, while superlatives agree with larger sets: "the larger of the two" vs. "the largest of the three". Some cases even involve suppletion: compare both, each other and between, which agree with noun phrases describing sets of two, with the corresponding forms all, one another, and among, used with noun phrases that describe sets of three or more.

The dual in the Baltic Languages

Among the Baltic languages, the dual form existed but is now nearly obsolete in standard Lithuanian. It can be occasionally found in poetic contexts and some dialects. The dual form Du litu was still used on two litas coins issued in 1925, but the plural form (2 litai) is used on modern two litas coins.

The dual in the Slavic languages

Common Slavic had a complete singular-dual-plural number system, although the dual paradigms showed considerable syncretism. Verbs had the same form in the second and third person dual; however, nouns, adjectives, and pronouns inherited the three Proto-Indo-European dual forms.^[6]

Of the living languages, only Slovene and Sorbian have preserved the dual number as a productive form. In all of the remaining languages, its influence is still found in the declension of nouns of which there are commonly only two: eyes, ears, shoulders, in certain fixed expressions, and the agreement of nouns when used with numbers.^[7]

In all the languages, the declension of the "two" maintains most of its dual characteristics, which can be verified from the table below.

Notes:

1. In some Slavic languages, there is a further distinction between animate and inanimate masculine nouns. In Polish, for animate masculine nouns the possible nominative forms are dwaj, dwóch, or dwu. The words oba and obidva meaning "both" are declined similarly to the numeral "two."
2. In Croatian, Serbian, and Sorbian, the forms given are for the genitive, since there is no locative form.

In Common Slavic, the rules where relatively simple for determining the appropriate case for the noun, when it was used with a numeral. The following rules apply:

1. With the numeral "one", both the noun, adjective, and numeral were in the same singular case, with the numeral being declined as an adjective.
2. With the numeral "two", both the noun, adjective, and numeral were in the same dual case. There were separate forms for the masculine and neuter-feminine nouns.
3. With the numerals "three" and "four," the noun, adjective, and numeral were in the same plural case.
4. With any numeral above "four", in the nominative case, the numeral was followed by the noun and adjective in the genitive plural case. For all other cases, both the noun, adjective, and numeral were in the same plural case.

With the loss of the dual in most of the Slavic languages, the above pattern now is only seen in the forms of the numbers for the tens, hundreds, and rarely thousands. This can be seen by examining the following table:

¹-sta is preferred in Serbian, -sto in Croatian for numbers 200 and 300; for numbers of 400 on, only -sto is used

In those languages that lost the dual, the following rules apply (except in Bulgarian and Macedonian, which have lost all declensions):^[9]

1. With the numeral "one", both the noun, adjectives, and numeral are in the same singular case, with the numeral being declined as an adjective.
2. With the numerals "two", "three" and "four", there are two different possibilities. In Polish, Czech, Slovak, Sorbian, and Ukrainian, the numeral, adjective, and noun are in the same nominative plural case. In Ukrainian, the stress on the noun is that of the genitive singular (or the old dual). In Russian, Belarusian, and Serbian and Croatian, the genitive singular is used for the noun, which in most cases resembles the dual in form is used. The adjective can be either in the genitive singular or plural forms. In all other cases, the appropriate plural form is used.
3. With the numerals "five" and above, in the nominative case, the numeral is followed by the noun and adjectives in the genitive plural case. For all other cases, both the noun, adjectives, and numeral are in the same plural case.

The resulting changes can be seen in the table below where the word "wolf" is used to form nominative noun phrases with various numerals.

The dual has also left traces in the declension of nouns describing body parts that humans customarily had two of, for example: eyes, ears, legs, breasts, and hands. Often the plural declension is used to give a figurative meaning. The table below summarizes the key such points.

Slovene

The Slovene language is the only major Slavic language that retains full grammatical use of the dual, including distinct dual forms for both nouns and verbs. The dual declension merges with the plural in certain nominal cases (e.g., genitive). Note that dual number is compatible with use of the pronoun oba(dva) or obe(dve) ("both").

Nominative case of noun "wolf", with and without numerals:

The dual is recognised by many Slovene speakers as one of the most distinctive features of the language and a mark of recognition, and is often mentioned in tourist brochures.

For verbs, the endings in the present tense are given as -va, -ta, -ta. The table below shows a comparison of the conjugation of the verb oddati, which means to give away and belongs to Class I in the singular, dual, and plural.

In the imperative the endings are given as -iva for the first person dual and -ita for the second person dual. The table below shows the imperative forms for the verb hoditi (to walk) in the first and second persons of the imperative (the imperative does not exist for 1^st person singular).

Languages with dual number

• Indo-European languages
  • Avestan
  • Scottish Gaelic (only nouns, only following the numeral for 'two')
  • Frisian (only pronouns in some North Frisian dialects)
  • Ancient Greek
  • Old Irish
  • Old Russian
  • Sanskrit
  • Slovene
  • Lower Sorbian
  • Upper Sorbian
• Uralic languages
  • Khanty
  • Mansi
  • Nenets
  • Sami languages
• Afro-asiatic languages
  • Akkadian (Assyrian and Babylonian)
  • Arabic : Classical and Modern Standard Arabic
  • Biblical Hebrew
  • Egyptian (including Coptic)
  • Maltese
• Inuktitut
• Quenya (not a natural language)
• American Sign Language
• M?ori (only the personal pronouns)
• Samoan (only the personal pronouns)

Notes

See also

• Grammatical number

cs:Dvojné ?íslo da:Dualis de:Dual (Grammatik) es:Número dual fr:Duel (grammaire) hr:Dvojina he:???? hu:Kett?s szám nl:Dualis no:Dualis nn:Dualis nds:Tweetall pl:Liczba podwójna pt:Dual (número gramatical) ru:???????????? ????? sl:Dvojina fi:Kaksikko sv:Dualis uk:?????? vec:Dual zh:??