Some time ago I posted a message asking about the origin of the Sanskrit dual ending -au. It was explained, as far as I can remember, as the reflex of an extra-long vowel caused by certain stress patterns, derived regularly from *-oh1 (or was it *-oeh1 or *-ooh1?). But there is a little matter that I seek insight on before I lay this issue to rest: in Old Norse the nom. acc. pl. neuter of "two" and "that" are tvau and thau. Wolfgang Krahe explained that these neuter forms are derived from original masculine nom. acc. dual forms, corresponding to Sanskrit dvau and tau, implying that the Sanskrit diphthongs derive from original u-diphthongs, since they are what appear in Old Norse. Is Krahe completely misguided? What is the explanation for the Old Norse -au neuter endings?
Andrew Jarrette