The category of dual can be reconstructed for
Proto-Indo-European, the ancestor of all
Indo-European languages, and it has been retained as a fully functioning category in the earliest attested daughter languages. The best evidence for the dual among ancient Indo-European languages can be found in Old Indo-Iranian (
Vedic Sanskrit and
Avestan),
Homeric Greek and
Old Church Slavonic, where its use was obligatory for all inflected categories including verbs, nouns, adjectives, pronouns and some numerals. Various traces of dual can also be found in
Gothic,
Old Irish, and Latin (more below). Due to the scarcity of evidence, the reconstruction of dual endings for Proto-Indo-European is difficult, but at least formally according to the
comparative method it can be ascertained that no more than three dual endings are reconstructible for nominal inflection. reconstruct the dual endings as: •
Nominative/
accusative/
vocative: *-h₁(e) •
Genitive/
ablative: *-h₁(e) / *-oHs •
Dative: *-me / *-OH •
Locative: *-h₁ow •
Instrumental: *-bʰih₁ The Proto-Indo-European category of dual did not only denote two of something: it could also be used as an associative marker, the so-called
elliptical dual. For example, the
Vedic deity
Mitrá, when appearing in dual form
Mitrā́, refers to both Mitra and his companion
Varuṇa. Homeric dual refers to
Ajax the Greater and his fighting companion
Teucer, and Latin plural is used to denote both the semi-god
Castor and his twin brother
Pollux. Beside nominal (nouns, adjectives and pronouns), the dual was also present in verbal inflection where the syncretism was much lower. Of living Indo-European languages, the dual can be found in dialects of
Scottish Gaelic, but fully functioning as a paradigmatic category only in
Slovene, and
Sorbian. 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).
Sanskrit The dual is widely used in Sanskrit. Its use is mandatory when the number of objects is two, and the plural is not permitted in this case, with one exception (see below). It is always indicated by the declensional suffix (and some morphophonemic modifications to the root resulting from addition of the suffix). For nouns, the dual forms are the same in the following sets of cases, with examples for the masculine noun (boy): • nominative/accusative: bālau • instrumental/dative/ablative: bālābhyām • genitive/locative: bālayoḥ In Sanskrit, adjectives are treated the same as nouns as far as case declensions are concerned. As for pronouns, the same rules apply, except for a few special forms used in some cases. Verbs have distinct dual forms in the three persons in both the ātmanepada and parasmaipada forms of verbs. For instance, the root pac meaning "to cook", takes the following forms in the dual number of the present tense, called laṭ lakāra: (In Sanskrit, the order of the persons is reversed.) The one exception to the rigidness about dual number is in the case of the pronoun asmad (I/we): Sanskrit grammar permits one to use the plural number for asmad even if the actual number of objects denoted is one or two (this is similar to the "royal we"). For example, while
ahaṃ bravīmi,
āvāṃ brūvaḥ and
vayaṃ brūmaḥ are respectively the singular, dual and plural forms of "I say" and "we say",
vayaṃ brūmaḥ can be used in the singular and dual sense as well.
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: the
nominative-
accusative-
vocative and the
genitive-
dative. By the fifth century BC, the dual had been lost in some dialects, and had become rare in those that retained it. In the
Attic dialect of
Athens (which formed the basis of
Classical Greek), its use depended on the author, and it was generally limited to certain
fossilized expressions. The dual fell out of use entirely by the fourth century BC, with the exception of the occasional intentional
archaism. In
Koine Greek and
Modern Greek, the only remnant of the dual is the numeral for "two", , , which has lost its genitive and dative cases (both , ) and retains its nominative/accusative form. Thus it appears to be undeclined in all cases. Nevertheless,
Aristophanes of Byzantium, the foremost authority of his time (early 2nd century BC) on grammar and style, and a staunch defender of "proper" High Attic tradition, admonishes those who write '
(') (dative, plural number) rather than the "correct" '
(') (dative, dual number).
Latin The dual was lost in Latin and its sister
Italic languages. However, certain
fossilized forms remained, for example, (twenty), but (thirty), the words / (both, compare Slavic / from earlier *abō / *abāi), / with a dual declension.
Celtic languages Reconstructed
Proto-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 '''' "two". Traces of the dual remain in
Middle Welsh, in nouns denoting pairs of body parts that incorporate the numeral two: e.g. (from "knee"), (from "ear"). In the modern languages, there are still significant remnants of dual number in
Irish and
Scottish Gaelic in nominal phrases containing the numeral or (including the higher numerals 12, 22, etc.). As the following table shows, and 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. 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 , Welsh , Cornish ). This process is not fully productive, however, and the prefixed forms are semantically restricted. For example, Breton ( Notes: • 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 , or . • Variant form for the masculine/neuter locative and instrumental in Serbo-Croatian: / . In Common Slavic, the rules were relatively simple for determining the appropriate case and number form of the noun, when it was used with a numeral. The following rules apply: • With the numeral "one", both the noun, adjective, and numeral were in the same singular case, with the numeral being declined as a pronoun. • 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. • With the numerals "three" and "four", the noun, adjective, and numeral were in the same plural case. • With any numeral above "four", the numeral was followed by the noun and adjective in the genitive plural case. The numeral itself was actually a numeral noun that was declined according to its syntactic function. 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: The Common Slavic rules governing the declension of nouns after numerals, which were described above, have been preserved in Slovene. In those Slavic languages that have lost the dual, the system has been simplified and changed in various ways, but many languages have kept traces of the dual in it. In general, Czech, Slovak, Polish and Ukrainian have extended the pattern of "three/four" to "two"; Russian, Belarusian and Serbo-Croatian have, on the contrary, extended the pattern of "two" to "three/four"; and Bulgarian and Macedonian have extended the pattern of "two" to all numerals. The resulting systems are as follows: • In Czech, Slovak, Polish and Ukrainian, numerals from "two" to "four" are always followed by a noun in the same plural case, but higher numerals (if in the nominative) are followed by a noun in the genitive plural. • In Belarusian and Serbo-Croatian, numerals from "two" to "four" (if in the nominative) are followed by a noun in a form originating from the Common Slavic nominative dual, which has now completely or almost completely merged with the nominative plural (in the case of Belarusian) or genitive singular (in the case of Serbo-Croatian). Higher numerals are followed by a noun in the genitive plural. • In Russian, the form of noun following the numeral is nominative singular if the numeral ends in "one", genitive singular if the numeral ends in "two" to "four", and genitive plural otherwise. As an exception, the form of noun is also genitive plural if the numeral ends in 11 to 14. Also, some words (for example, many measure words, such as units) have a special "
count form" (счётная форма) for use in numerical phrases instead of genitive (for some words mandatory, for others optional), for example, восемь мегабайт, пять килограмм and пять килограммов, три ряда́ and три ря́да, and полтора часа́. • In Bulgarian and Macedonian, all numerals are followed by a noun in a form originating from the Common Slavic nominative dual, which has now been re-interpreted as a "count form" or "quantitative plural". These different systems are exemplified in the table below where the word "wolf" is used to form nominative noun phrases with various numerals. The dual and forms originating from it are underlined. 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. Some scribes of
Old Church Slavonic used
graphic variants of O when writing forms of "eye", contrasting singular , "eye" with dual or , "[two] eyes". The difference was graphic, not in pronunciation.
Slovene Along with the
Sorbian languages,
Chakavian, some
Kajkavian dialects, and the extinct
Old Church Slavonic,
Slovene uses the dual. Although popular sources claim that Slovene has "preserved full grammatical use of the dual," Standard Slovene (and, to varying degrees, Slovene dialects) show significant reduction of the dual number system when compared with Common Slavic. In general, dual forms have a tendency to be replaced by plural forms. This tendency is stronger in oblique cases than in the nominative/accusative: in standard Slovene, genitive and locative forms have merged with the plural, and in many dialects, pluralization has extended to dative/instrumental forms. Dual inflection is better preserved in masculine forms than in feminine forms. Natural pairs are usually expressed with the plural in Slovene, not with the dual: e.g. "hands", ears. The dual forms of such nouns can be used, in conjunction with the quantifiers "two" or "both", to emphasize the number: e.g. "I only have two hands". The words for "parents" and "twins" show variation in colloquial Slovene between plural (, ) and dual (, ). Standard Slovene has replaced the nominative dual pronouns of Common Slavic ( "the two of us", "the two of you", "the two of them" [m./f./n.]) with new synthetic dual forms: (literally, "we-two"), , . 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 , , . The table below shows a comparison of the conjugation of the verb , which means "to do, to make, to work" and belongs to Class IV in the singular, dual, and plural. In the imperative, the endings are given as for the first-person dual and for the second-person dual. The table below shows the imperative forms for the verb ("to walk") in the first and second persons of the imperative (the imperative does not exist for first-person singular).
Sorbian language As in Slovenian, the Sorbian language (both dialects Upper and Lower Sorbian) has preserved the dual. For nouns, the following endings are used: • The genitive form is based on the plural form of the noun. • The -e ending causes various softening changes to occur to the preceding constant, for further information see the article on
Sorbian. For example, the declension of
sin (masculine) and
crow (feminine) in the dual in Upper Sorbian would be given as For verbs, the endings in the present tense are given as , , . The table below shows a comparison of the conjugation of the verb , which means "to write" and belongs to Class I in the singular, dual, and plural. == Languages with dual number ==