Nothing confuses English speakers more than French possessive adjectives.
The key to understanding how to use them is rather simple: you need to focus on the thing you are describing, NOT who it belongs to.
In English, you use the possessive adjective according to the gender (male or female) of the subject.
To describe one male dog who belongs to one man, you would say “his dog”.
To describe a female dog who belongs to one man, you would still say “his dog”.
To describe two dogs who belong to one man, you would say “his dogs”.
It doesn’t matter in English whether the dogs are female or male, or whether there is one or several dogs. Because the dogs belong to a man (in this example) they will always be “his”.
So you could say there is a single logic: who is the subject? I, you, he, she, they? Then it’s my, your, his, her, their. Very simple.
In French, it’s not that easy because the dog actually matters. Actually, both the person who owns the dog and the dog matter. It’s a double logic.
First, you have to choose the appropriate adjective according to the owner. Just like in English. But unlike English, you then have several possibilities.
For je – mon, ma, mes
For tu – ton, ta, tes
For il and elle – son, sa, ses (so unlike English, we don’t differentiate between “his” and “her”... oh the irony!!)
For nous – notre, nos
For vous – votre, vos
For ils and elles – leur, leurs
Then, you have to take into consideration the dog(s)!
Is the dog male or female?
Is there one or several dogs?
This step is how you will finalise your choice of French possessive adjective.
Mon, ton, son, notre, votre, leur = One dog, masculine.
Ma, ta, sa, notre, votre, leur = One dog, feminine
Mes, tes, ses, nos, vos, leurs = several dogs (in plural, it doesn’t matter whether the dogs are feminine or masculine).
M’, t’, s’ are never used for possessive adjectives.
Remember that in French things have a gender too. So for example, “une voiture” is feminine.
John would say: ma voiture.
English speakers find this very weird on so many levels!
So, to make it clear, let’s see some examples:
If John has a female dog he will say: ma chienne. (not mon. It doesn’t matter whether John is a boy or a girl, what matters is that John is a “je” and then that he has just one female dog).
If Mary has three dogs, she will say: mes chiens. (Mary speaks so she is a “je” and there are several dogs).
If Mary and John have one male dog together, they will say: notre chien (Mary and John speak, so they are a “nous”. Even though there are two owners, what matters is there is only one male dog).
In other words, to master French possessive adjectives, you have to focus on the dog!