sa vs. son
they are both his or hers, but I can't figure out when you use which. Is it a m/f thing? Thank you!
Yes is a masculine/feminine thing. In French the possessive determiners have to agree with the gender of the noun phrase, not the with gender of the owner.
You use mon in front of masculine words, and ma for feminine words.
She has her book - Elle a son livre - un livre (m) He has his soup - Il a sa soupe - une soupe (f)
but!! Feminine words starting with a vowel or silent h, use son too!
He has his plate - Il a son assiette - une assiette (f)