La famille

French spends enormous energy on the distance between tu and vous, then makes one blanket exception: family. Parents, grandparents, brothers, sisters, cousins, children. All tu, from the start, with no ceremony about it.

No, really, all of them

Learners often assume grandparents must be vous, on the reasoning that they are older and deserve the respect. They are not. A French child says tu to their grandmother from the moment they can speak, and is still doing it at forty.

Families who use vous with parents do exist. They are usually old and usually wealthy, and other French people find it as noteworthy as you would. If you ever meet one, someone will make a point of telling you.

The words hide a trap

Beau-père is your stepfather and your father-in-law. Belle-mère covers both on the other side. French does not distinguish them, so context has to carry it, which occasionally produces a sentence nobody can parse without asking a follow-up question.

Parent is wider than the English word. Mes parents is your mother and father, but un parent on its own can be any relative at all. If you mean a cousin rather than a father, say which.

Where tu extends to

Beyond the family, tu reaches further than you might expect:

• Children, always, whoever they belong to
• Fellow students, generally from the first day
• People roughly your own age somewhere obviously informal, a party or a hostel

The genuinely awkward case is a colleague your own age. That stays vous until you are told otherwise, however strange it feels, and there is a whole session on why.

One that sounds wrong and is not

On does most of the work of nous in spoken French, and with family it has all but replaced it. On va manger is what a French family says at the table. Nous allons manger is what a textbook says. Both are correct; only one gets used.