I know that many people think the sound changes that occur in pet forms are related to which sounds small children have the most difficulty learning to pronounce properly when they are first learning the speak.
"R" is one of the harder sounds for children to learn, and "d" is a common substitute for it. Back in medieval times
Dick, Dob, and Dodge were among the common pet forms for
Richard,
Robert, and
Roger. So it's no surprise that the "r" in
Sarah would change to "d".
As for the vowel in the first syllable -- I think that in some accents of English "
Sarah" does sound like "Say-ruh" even today.
I have never heard of
Posie being a general pet form for
Josephine before. Have you actually known more than one woman who used this? In individual families all sorts of unique things could happen. :) It does seem to be just a rhyming form based on
Josie, though.
P.S. I was very surprised after I wrote the above to find that the explanation for
Posy on this site is "diminutive of
Josephine." I would still think that a rhyming form based on
Josie is the best explanation.
This message was edited 2/10/2014, 6:23 AM