[2][3][4] Several historical linguists have pointed towards the apparent material and social continuity connecting the cultures of the Nordic Bronze Age (1800 – 500 BC) and the pre-Roman Iron Age in Northern Europe (500 BC – 1 AD) as having implications in regard to the stability and later development of the Germanic language group.
[a] The emerging consensus among scholars is that the First Germanic Sound Shift, long considered to be the defining mark in the development of Proto-Germanic, happened as late as 500 BC.
[7][8][9] Research conducted over the past few decades displays a notable interest in exploring the linguistic and sociohistorical conditions under which this sound shift occurred, and often formulates theories and makes reconstructive efforts regarding the periods immediately preceding Proto-Germanic as traditionally characterised.
[c] The upper boundary (earliest date) assigned to the Germanic parent language is described as "dialectal Indo-European".
"[16] Other rules thought to have affected the Pre-Germanic stage include Cowgill's law, which describes the process of laryngeal loss known to have occurred in most post-PIE (IE) dialects, and Osthoff's law, which describes rules for the shortening of long vowels, known to have applied in western dialects such as Greek, Latin, and Celtic, but not in Tocharian or Indo-Iranian.