Northwest Germanic is a proposed grouping of the Germanic languages, representing the current consensus among Germanic historical linguists. It does not challenge the late 19th-century tri-partite division of the Germanic dialects into North Germanic, West Germanic and East Germanic, but proposes additionally that North and West Germanic (i.e. all surviving Germanic languages today) remained as a subgroup after the southward migration of the East Germanic tribes, only splitting into North and West Germanic later. Whether this subgroup constituted a unified proto-language, or simply represents a group of dialects that remained in contact and close geographical proximity, is a matter of debate, but the formulation of Ringe and Taylor probably enjoys widespread support:
There is some evidence that North and West Germanic developed as a single language, Proto-Northwest Germanic, after East Germanic had begun to diverge. However, changes unproblematically datable to the PNWGmc period are few, suggesting that that period of linguistic unity did not last long. On the other hand, there are some indications that North and West Germanic remained in contact, exchanging and thus partly sharing further innovations, after they had begun to diverge, and perhaps even after West Germanic had itself begun to diversify.
This grouping was proposed by Hans Kuhn as an alternative to the older view of a Gotho-Nordic versus West Germanic division. This older view is represented by mid 20th-century proposals to assume the existence by 250 BC of five general groups to be distinguishable: North Germanic in Southern Scandinavia excluding Jutland; North Sea Germanic along the middle Rhine and Jutland; Rhine-Weser Germanic; Elbe Germanic; and East Germanic. The Northwest Germanic theory challenges these proposals, since it is strongly tied to runic inscriptions dated from AD 200 onwards.
Most scholars agree that East Germanic broke up from the rest of the languages in the 2nd or 1st centuries BC. The Runic Inscriptions (being written from the 2nd century) may mean that the north and West broke up in the 2nd and 3rd centuries. The Migration Period started around the 4th and 5th centuries; an event which probably help diversify the Northwest Germanic (maybe even the West Germanic) languages even more. The date by which such a grouping must have dissolved—in that innovations ceased to be shared—is also contentious, though it seems unlikely to have persisted after 500 AD, by which time the Anglo-Saxons had migrated to England and the Elbe Germanic tribes had settled in Southern Germany.
Postulated common innovations in North Germanic and Gothic, which therefore challenge the Northwest Germanic hypothesis, include:
A minority opinion is able to harmonize these two hypotheses by denying the genetic reality of both Northwest Germanic and Gotho-Nordic, seeing them rather as mere cover terms indicating close areal contacts. (Such areal contacts would have been quite strong among the early Germanic languages, given their close geographic position over a long period of time.) Under such an assumption, an early close relationship between Nordic and Gothic dialects does not exclude a later similar relationship between remaining North and West Germanic groups, once the Gothic migration had started in the 2nd or 3rd century.
There are also common innovations in Old High German and Gothic, which would appear to challenge both the Northwest Germanic and the Gotho-Nordic groupings. However, these are standardly taken to be the result of late areal contacts, based the cultural contacts across the Alps in the 5th and 6th centuries, reflected in the Christian loanwords from Gothic into Old High German.