Unidirectionality hypothesis

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. 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. 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. 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.