Richard Wordingham wrote:
> But the present singular has prad- - prad, prazi, prádã. The -ã- is
> what one should expect from the lack of stress.
Actually, we don't need a /p-/ to produce -ã- in the weak stem. The /r/
itself conditions the retraction of pretonic *e, cf. rãs,inã < resi:na.
This suggests that *pread- was replaced by <prad-> because of the
derivational ambiguity of its unstressed alomorph <prãd->.
It's like Mod.E cloth : clothes (as if the long vowel of the latter had
been produced by ME open-syllable lengthening, while in fact the
original vowel was long and the irregular shortening in <cloth> is
analogical, cf. <staff> : <staves>).
Piotr