The tips for skill "Genitive" state that plural genitive forms would be easy, but in the examples they give there is a shift of the accent from the second syllable in οι γυναίκες to the third in των γυναικών, while it remains on the first in οι σκύλοι -> των σκύλων and on the last in τα παιδιά -> των παιδιών.
My question is: When does this happen? Is it predictable in some way?
I tried to look up a few more words, but I don't really get the pattern yet.
Accent shifted:
οι ελέφαντες -> των ελεφάντων
οι πίθηκοι -> των πιθήκων
οι άνδρες -> των ανδρών
τα φίδια -> των φιδιών
τα αχλάδια -> των αχλαδιών
Not shifted:
οι παππούδες -> των παππούδων
οι αρκούδες -> των αρκούδων
τα μήλα -> των μήλων