I recall a male student once lamenting over a faux pas he'd committed when he'd met his French girlfriend's father and addressed him using the 'tu' form. His bride-to-be was naturally shocked as to her it sounded over-familiar and rude - as though he'd called him, "Mate!" or "Buddy!".

The French father could have answered,

Better translations might be, I didn't realise we knew each other so well or Since when have we been that close? - the set answer when you want to put someone overly familiar in their place.
In this case, the father probably just smiled quizzically, leaving the young man somewhat perplexed as to what he'd done wrong. Not a good start to the blossoming of a new Franco-British relationship.

Using the right form when addressing someone for the first time is in fact about much more than just making the correct choice between formal and informal. It signifies how close the relationship is and also denotes the appropriate level of respect.

Navigating through this maze is very difficult for English speakers who only have the universal you. The right form of address recognises an underlying protocol which is learned through habit rather than by formal teaching and is a topic of much discussion over the Internet.

Historical background

Over time there have been several attempts to abolish the use of vous.

One attempt was after the French Revolution of 1789, when a decree banning the use of vous and its royal connotations was introduced in 1793. The 'tu' form was considered to be the equivalent of the socialists' use of 'comrade'.

Another effort was made in 1968, when the students (known as the generation les soixante-huitards - the 68 ones) wanted to break down boundaries and consequently favoured the use of tu.
Both attempts failed, probably because the use of vous is so anchored in the psyche of the French and because it is still the quickest way to demonstrate your respect for others and show your breeding. These unspoken signs are not ready to die out.

One of the slogans written on the walls of the Sorbonne in 1968:

Tu and Vous in family situations

Normally in most French families, the tu form is used to address each other - mother to father, parent to child, child to parent, aunt to niece, nephew to aunt, cousin to cousin, etc. In some old bourgeois families, the vous was used between parents and their offspring and between husband and wife but this was very rare and used primarily to stand out from the hoi polloi. Most famously, General De Gaulle and Jacques Chirac were known to say vous to their wives.

Your in-laws would usually be addressed by the vous form, but this varies according to specific family traditions. What happens in my family might be different to the one next door, but a tacit agreement will be made between the interested parties, the older deciding on what is acceptable.
For instance, in my family, my mother always used tu with my sister-in-law whom she had known as a child but my sister-in-law said vous back to my mother out of respect, although as a child she would have used the tu form.

You would also use tu with your friends of a similar age to you, whatever age you are, but you would use the 'vous' form to their parents, even if you have known them as long as their children.

School/ Further Education

In primary schools, and up to about the age of nine, a pupil would say tu to the teacher and the teacher would reciprocate. After that, the norm is that the pupil would say vous to the teacher and the teacher would carry on saying tu to the pupil.

In France, it's customary to address your teachers by the respectful 'vous' form and from secondary school onwards this will be the norm, whatever the age of the teacher and the teacher will reciprocate.

In further education, the 'vous' form, and the even more formal Monsieur, Madame, Mademoiselle, will be used by students to address any member of the staff. This creates the necessary distance between them for the establishment to function in a proper French manner.
The students will say tu to each other even if they don't know each other, unless one of them is considerably older, in which case the 'vous' form would be used but such a situation is unlikely.

The teaching staff will have their own traditions according to hierarchy, prior knowledge of each other and the overall culture of the school. It will also depend on age, gender and rank but the way they address each other will show a certain level of respect and deference, based on the nature of the friendship or relationship.

But as a rule, teachers will say vous to their boss and tu to each other.

Work/Business

Until the 1970s, the world of business was dominated by the 'vous' form although there were some exceptions.

Tu might have been used with a subordinate but it would show disrespect. If you had worked for decades with a colleague who was on a similar level to you in the company, then you might have said tu to them.
Interestingly, a boss might have called their secretary by their Christian name but still used the 'vous' form, as tu might have been construed as a step too far and given the wrong idea to others altogether!

Change occurred in the 1970s - 1990s, when the use of tu made its way into the sphere of French business, probably as a result of the soixante-huitards* (see historical note) and the influence of "management à l'américaine". Tu can be seen as the equivalent of being on first-name terms in Anglo-Saxon cultures.
It soon became de rigueur in start-ups and IT companies. Although in more traditional companies like the banking sector, old-fashioned customs remain and tu can be construed as rude.

In an average company, the general company culture will see colleagues of a similar age and background saying tu to each other right from the start but saying vous to their boss and to older colleagues.

An employee of Auchan Supermarkets (who is also a Union Rep) points out that although everyone uses the tu form within the company, when he is acting in negotiating activities with the bosses, he expects them to address him with the vous form as a mark of respect and to create some distance between them.

It's interesting to note that in the Sales department, Sales staff are discouraged from using the 'tu' form when selling as it comes over as too familiar, rude and off-putting, unless a well-known client suggests being more informal and using the 'tu' form.

Often the first rule that a new employee may learn on joining a company is whether they use tu or vous, for example:

Tu and vous can be used as linguistic tools to signify proximity or distance within a relationship. It's important that everyone abides by the rules because tu can be used to patronise subordinates.

So, it all depends on company culture and the degree of respect you wish to show the person you're talking to. Hierarchy, education, age, gender, milieu, and type of work all have a bearing. However, it would appear that vous is trying to make a come-back in the business world.

Examples from the media

The principles of respect and deference as denoted by the correct form of address in life are well represented in the media and it's interesting to note what happens in films and on TV.

For instance, in old-fashioned films, a courting couple would say vous to each other until they became intimate, just as in real life.
Or, in the context of a hold-up (un braquage), the perpetrator would use tu to talk to his victim. If someone had a gun to your head, they wouldn't say vous to you even if they'd never seen you before in their life! But it would be in your best interest to say vous to them to show your respect!

I was watching season 7 of "Engrenages" (Spiral in English) the other day, and I came across an interview scene between a fifteen-year-old suspect (with a lawyer in attendance) and an inspector.
The lawyer objected to the use of the tu form by the policeman, when questioning the young suspect, as not being respectful enough. The translation of the subtitles was interesting and went something like:

and the subtitle read as "Can you show a bit more respect for my client?"
In this context, the police (who are often criticised by the public for being overfamiliar) were using tu as a tool to intimidate the suspect.

I was also watching a film called "Sage-femme" (The Midwife) which illustrates the intricacies of vouvoiement and tutoiement well. It's about the relationship between an older woman, Béatrice (Catherine Deneuve) and a younger woman, Claire (Catherine Frot) whom she knew as a child, Béatrice having been the lover of Claire's deceased father.

It's obvious that when Claire was a child she used to say tu to Béatrice but now uses vous as they've been estranged for 30 years and Claire is now an adult. Claire resents and blames Beatrice for the trauma that has happened to her since she walked out on her father. She's now a mother herself and works as a midwife.
Here's an excerpt from the dialogue:

Eventually by the end of the film, they're able to use tu with each other when they are getting on better.

Twitter and other social media platforms are the perfect forum for the tu form as they reflect the informal way young people address each other. Most comments are made in the tu form there but there is little evidence that this is going to transcend entrenched French social mores completely, as outlined in this BBC article.

It's also interesting to note that on dating sites, a woman in her forties prefers her suitors to use the vous form, the tu being seen as over-familiar and rude - even in the 21st century!

Asking permission

A key aspect is who instigates the change of register. Here are some rules as to who suggests the first move from vous to tu.

I had a very Gallic reaction the other day to this very question. I am after all, "une femme d'un certain âge". I was invited for the first time to visit a local informal French language conversation group as a native speaker. A male student, Alan, of a similar age to me, was hosting it at his house. Now, I didn't know Alan from Adam but he said right at the start,

It wasn't even a question, and faced with this fait accompli, I sort of agreed under my breath but the image of us not raising pigs together did float in my mind ... I still found it quite shocking as this would never have happened in France. A gentleman would always wait for a lady to make the suggestion. He, of course, was totally unaware of his faux pas although I did carry on saying vous to him.

In short, don't ask to use the tu form of a "superior" or "older" person; it's up to them to make the suggestion and you risk being considered rude or presumptious if you ask. If you're the "superior/older" person, then you can suggest using the tu form by saying something like -

But never the other way round.

Summary

In short, you would normally say vous to a person older than or superior to you (in a formal hierarchy) or to someone unknown to you.

So you use vous to talk to someone in the street or someone you sit next to on a plane, a train or a bus. The same applies in shops, whether in the local shops or to cashiers at the supermarket or in your dealings with doctors, dentists or lawyers.

Young people say tu to each other right from the start, even if they don't know each other, as though they were members of the same club, since being a similar age is the determining factor. This also applies to colleagues who are graduates from the same university or grande école.

Normally, an adult will use tu with a child even if the child is unknown to them.

Tu is also used to address pets unless you want to use vous for comic effect.

During my research, the word I heard most in association with the use of the vous form was respect. Using the wrong form can equate to rudeness, even causing offence at times.

The lesson my student, mentioned at the start, should have learnt is that when in doubt, it's always safer to use vous. And to wait for the older person, i.e. his girlfriend's father, to give the go-ahead for a closer relationship!