I think - though not sure - that it’s because ‘bydded’ has a sense of wanting something to happen - let it be this way, so it’s a bit like “Dw i’n moyn (dw i isio) i’r hen iaith barhau” where you want the ‘hen iaith’ to do something - parhau.
that really makes sense, thanks.
… if a verb is part of the next clause
“Y bydded y noswaith honno yn unig, ac na fydded gorfoled ynddi”
I don’t know if this will help.
I looked up Exodus 13:9 in a few versions -
William Morgan version: A bydded i ti yn arwydd ar dy law
Cymraeg Newydd version: Bydd hyn i ti yn arwydd ar dy law
NIV (English): This observance will be for you like a sign on your hand.
So, I’m wondering if “Bydded i ti” just means " will be to you" So, perhaps it’s as simple as the “i” just meaning “to”.
Clwb cya yn y bore bendegeddig pace and level fab for listening x