þeir

The English third-person plural pronouns — they, them, their — are Old Norse, not Old English. This is a remarkable fact because pronouns are among the most resistant words in any language to replacement: they are used so constantly, are so structurally embedded, that foreign words almost never displace them. Yet in English, the Norse forms completely replaced the Old English ones. The Old English third-person plural nominative was hie (they), the dative was him (them), and the genitive was hira (their). In the Danelaw, where Norse and Old English speakers lived in close contact, the Norse pronouns þeir (they), þeim (them), and þeirra (their) entered English and, over the course of the twelfth through fourteenth centuries, displaced the Old English forms entirely.

Why did the pronouns change? The most compelling explanation is phonological confusion. Old English hie (nominative plural) sounded dangerously like he (nominative singular masculine), and the Old English him (dative plural) was identical to him (dative singular masculine). The Norse forms, beginning with the unmistakable TH- sound, were unambiguous: they sounded nothing like the singular forms. This clarity made them useful even to English speakers who were not themselves Norse — the Norse pronouns solved a real ambiguity in Old English grammar. The replacement was aided by the prestige of the Danelaw settlements and the sheer quantity of Norse-English contact.

The shift happened gradually from north to south, following the Danelaw geography. Northern English texts show þe- forms (they, them, their) by the twelfth century. Southern English held onto the hie/him/hira forms longer, and the final stages of the transition coincide with the major dialect leveling and standardization of English in the fourteenth and fifteenth centuries. Chaucer, writing in the 1370s–1390s, uses both the Norse they/them/their forms and occasionally the older hem for them. By the fifteenth century the Norse forms are universal in standard English.

The grammatical depth of this borrowing is hard to overstate. Languages borrow nouns readily, verbs with more difficulty, and function words — pronouns, prepositions, conjunctions — almost never. The complete replacement of a language's third-person plural pronoun system is, in documented linguistic history, essentially unique. English did it because the Norse contact in the Danelaw was not superficial cultural exchange but deep, sustained, multilingual community life — farming communities, towns, markets where Old English and Old Norse speakers lived, worked, and intermarried across generations.