In French, possessive adjectives (my, your, his, her, our, their) agree with the noun they describe, NOT with the person it belongs to.
It means that if you are talking about ‘his table’, in English, the emphasis is put on the fact that the possessor is masculine. In French, the possessor does not matter; because ‘une table’ is feminine, you have to use the feminine possessive adjective ‘sa’.
The gender of the noun
To use the correct possessive adjective, you need to know the gender of the noun you want to describe.
➤ You use ‘son’ in both cases because ‘manteau’ is masculine and it doesn’t matter who it belongs to.
his teddy bear
her teddy bear
➤ You use ‘son’ in both cases because ‘peluche’ is feminine and it doesn’t matter who it belongs to.
‘une chanson’ (a song) is feminine.
ma chanson : my song
ta chanson : your song (singular, informal)
sa chanson : it could be translated by his or her song depending on the context
notre chanson : our song
votre chanson : your song (formal)
leur chanson : their song
‘un livre’ (a book) is masculine.
mon livre : my book
ton livre : your book (singular, informal)
son livre : it could be translated by his or her book depending on the context
notre livre : our book
votre livre : your book (formal)
leur livre : their book
Before a vowel
Watch out for ‘ma’, ‘ta’, ‘sa’ when they describe a feminine noun that starts with a vowel. To avoid having two vowels next to each other, their masculine version ‘mon’, ‘ton’, ‘son’ is used.
‘une imprimante’ (a printer) is feminine.
The accurate possessive adjective should be ‘sa’ but because ‘imprimante’ starts with a vowel, you swap ‘sa’ for ‘son’.
son imprimante : his/her printer
In a nutshell…
|masculine||feminine||before a vowel||plural|
|his, her, its||son||sa||son||ses|
(plural or formal)