The old guideline was tu for children and animals, vous for everyone else.
But that doesn’t hold true any more. Just where are you in your relationship? Get it wrong either way, and you’re likely to raise hackles.
Speaking in very broad terms, tu is more left-wing, more egalitarian, revolutionary, young and groovy – vous is more traditional, more right- wing, more conventional, perhaps a little more stolid.
Groovy 68ers (the generation who protested for social freedoms in 1968) feel like you’re relegating them to a retirement home if you drop a respectful vous into the conversation, but your stuffy bank manager might think you’re not treating her with respect if you use tu.
Dogs, luckily, don’t appear to care either way.
It gets stranger, however, when you consider that the Chiracs famously continued to vouvoyer each other throughout their marriage – all six decades of it.
This isn’t apparently that rare, either. My postman says that using vous to your lover has the same curiously erotic appeal as thick-rimmed glasses and a demure blouse. Don’t ask how that conversation started.
Vous is formal, it underlines the distance between two people, it makes conversations deliberately more distant.
When I first arrived in France I didn’t know any of this. I just used vous all the time because I wasn’t acquainted with any children or dogs.
I got used to it, and felt safe with it. No one could think I was taking liberties, no one could accuse me of lacking respect. Everything went well until people started giving me permission to use tu – for one thing, it felt strange, and for another, I forgot who to vous and who to tu.
And slipping up is not good.
I once accidentally used tu to a very talented and friendly carpenter who was working at the house, and the result was immediate: he looked like an outraged hedgehog.
I immediately apologised, and he accepted my excuses, but he remained visibly ruffled for the rest of the day.
On the other hand, the lovely baker I go to uses tu to everyone, and when I absent-mindedly used vous, she looked quite upset. Had she done something to offend me, she wanted to know?
Another weird one is in French churches. People tend to use tu when talking to God, but vous when talking to a priest or to the Virgin Mary.
But even that varies. The postman says it depends on your relationship with Mary.
He says his mother is on tutoying terms with the Mother of God, but that personally he sticks with vous (I’m trying hard to forget the comments about the eroticism of thick-rimmed glasses now).
And all that is without the added complexities of calling dogs and children tu but having to remember to switch to vous when you acquire a second dog or a second child.
It’s a never-ending conundrum, but luckily it isn’t only foreigners who are confused.
French magazines regularly carry advice columns about it, and the debate continues online: to tu or not to tu, that is the question...