Isaac (G. R.): Vocative plural of masculine *(y)o-stems in Old Irish.
In ZCP 49–50 (1997), pp. 333–340.
Challenges the view that the voc. pl. ending -(i)u continues PIE nom. pl. * -ōs, and argues that although both nom. and acc. plural were replaced by the pronominal endings in Old Irish the acc. pl. took over from the voc. pl. to avoid confusion with the voc. sg.