Very early in Middle English, texts especially in the North and East, tend to use a suffix spelled –(e)s for noun plurals, while in Southern texts the suffix –(e)n of the Old English weak declension at first spreads, but then by 1250 also yields to –(e)s. This sibilant plural has remained productive in English ever since. This essay shows on phonological grounds that the vocabulary item for this nominal plural must be –lexically specified as +Voice. That is, the voicing is not due to any synchronic assimilation process. The source of this underlying voiced sibilant –z, completely absent in Old English, comes from the genealogical ancestor of Middle English, Common Scandinavian, whose non-neuter plural in structural case is precisely this segment –z Haugen 1982. This essay argues that this form was an integral part of the Norse brought to England by Scandinavian settlers in the ninth century. The later change in Mainland Scandinavian of this –z to –r, completed in the twelfth century, failed to establish itself in the Anglicized Norse of England, due to sociolinguistic factors akin to those set out in Labov 1963.