Unidirectionality hypothesis

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In linguistics, the unidirectionality hypothesis proposes that grammaticalisation works in a single direction. That is, pronouns may fuse with verbs, or prepositions may fuse with nouns, to create new inflectional systems, but inflectional endings do not break off to create new pronouns or prepositions.

Linguistics is the scientific study of language. It involves analysing language form, language meaning, and language in context. The earliest activities in the documentation and description of language have been attributed to the 6th-century-BC Indian grammarian Pāṇini who wrote a formal description of the Sanskrit language in his Aṣṭādhyāyī.

In linguistics and grammar, a pronoun is a word that substitutes for a noun or noun phrase. It is a particular case of a pro-form.

Inflection modification of a word to express different grammatical categories such as tense, mood, voice, aspect, person, number, gender and case

In grammar, inflection is the modification of a word to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, and mood. It is found in many but not all languages. The inflection of verbs is also called conjugation, and one can refer to the inflection of nouns, adjectives, adverbs, pronouns, determiners, participles, prepositions, postpositions, numerals, articles etc., as declension.


The unidirectionality hypothesis does not claim that linguistic change will occur in any particular instance, only that if it does occur, it will be in the direction of lexical word to grammatical word and not the other way around.

Certain schools of linguistics object to the unidirectionality hypothesis on theoretical grounds, believing that there should be no favoured direction in the evolution of grammatical forms, and have proposed numerous counter-examples. However, most of these proposals show a lack of understanding of the hypothesis or of the history of the languages in question, and are instead examples of lexicalisation. True counter-examples to unidirectionality appear to be rare and require unusual conditions.

A counter-example

One counter-example is the evolution of a new pronoun for "we" out of verbal conjugations in northern dialects of Irish Gaelic. It's as if Spanish hablamos (we speak) were reanalyzed as habla mos, with mos becoming a new pronoun "we" that replaced the existing pronoun nosotros. In Irish this required a rather special set of circumstances.

Irish language Goidelic (Gaelic) language spoken in Ireland and by Irish people

Irish is a Goidelic (Gaelic) language originating in Ireland and historically spoken by the Irish people. Irish is spoken as a first language in substantial areas of counties Galway, Kerry, Cork and Donegal, smaller areas of Waterford, Mayo and Meath, and a few other locations, and as a second language by a larger group of non-habitual speakers across the country.

Spanish language Romance language

Spanish or Castilian is a Western Romance language that originated in the Castile region of Spain and today has hundreds of millions of native speakers in the Americas and Spain. It is a global language and the world's second-most spoken native language, after Mandarin Chinese.

Unusually for a European language, Irish is verb-initial, as can be seen in phrases such as

Chonaic mé thú "I saw you" (literally saw I thee).

In Old Irish the verb was inflected for person, as it still is in the south of Ireland. The verb 'to be' was inflected as follows:

Old Irish is the name given to the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from c.600 to c.900. The primary contemporary texts are dated c.700–850; by 900 the language had already transitioned into early Middle Irish. Some Old Irish texts date from the 10th century, although these are presumably copies of texts composed at an earlier time period. Old Irish is thus forebear to Modern Irish, Manx, and Scottish Gaelic.

to be
(Old Irish)

With such a system, there was no need for pronouns except for emphasis, as is the case with Spanish today. However, in the north of Ireland, the system eroded, and most of the inflectional endings disappeared. The use of the subject pronouns then became obligatory to disambiguate the person of the verb. A similar change has taken place in French, where the loss of most of the verbal endings (in the spoken language at least) has meant that subject pronouns are now required.

French language Romance language

French is a Romance language of the Indo-European family. It descended from the Vulgar Latin of the Roman Empire, as did all Romance languages. French evolved from Gallo-Romance, the spoken Latin in Gaul, and more specifically in Northern Gaul. Its closest relatives are the other langues d'oïl—languages historically spoken in northern France and in southern Belgium, which French (Francien) has largely supplanted. French was also influenced by native Celtic languages of Northern Roman Gaul like Gallia Belgica and by the (Germanic) Frankish language of the post-Roman Frankish invaders. Today, owing to France's past overseas expansion, there are numerous French-based creole languages, most notably Haitian Creole. A French-speaking person or nation may be referred to as Francophone in both English and French.

The subject pronouns of modern Irish are the following:


These were added to the verb wherever the inflections had disappeared. Since the subject comes after the verb in Irish, the pronouns effectively replaced the old verbal endings:

to be
1táim or
tá mé
2tá tútá sibh
3tá sé,
tá sí
tá siad

The first-person singular ("I") form is still retained in some areas but appears to be in the process of dropping out and being replaced by the pronoun . However, the first-person plural ("we") formthe only ending that was a complete syllableis robust everywhere, and the pronoun sinn is not used in this situation. This happened not just with the verb 'to be' but with all Irish verbs.

The unidirectionality hypothesis would predict that this paradigm would either remain as it is, with the pronouns retaining their status as independent words, or else that they might fuse with the verb into a new verbal conjugational system, as existed in Old Irish. However, something more unusual occurred: the pronouns did retain their separate status, but the first-person plural verbal ending -mid was reanalyzed as a pronoun, by analogy with the other persons. Thus Irish has acquired a new pronoun for "we", muid, which can be used as an independent word, for example as an emphatic muide "us": If someone asks "Who is there?", an Irish speaker might reply, Is muide ("It is us"). This new pronoun appears to be replacing the original pronoun sinn.

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