I’ve just got back from across the Channel, where the flavory business of salutation isn’t all just about the obligatory kissing on both cheeks, but also involves a potpourri of expressions to use at different times of the day in different contexts and settings — but largely as goodbyes rather than hellos.
In English, apart from our general hi or hello, we have four time-specific salutations: “good morning”, “good afternoon”, “good evening”, and “good night” — the latter one usually expressed as a farewell or sign-off rather than a late-evening howdy. The first and last are common in many settings, both informal and formal, spoken and written. We’re used to greeting anyone at the beginning of the day with “good morning”, and “good night” is standard between acquaintances, friends, family or lovers — whatever the circumstances of the parting (or even just before going to sleep). But “good afternoon” and “good evening” have a more limited usage, tending to be reserved for semi-formal or formal occasions — such as at a public presentation or in a broadcast, as a written greeting, or when talking to someone on the phone. You would be unlikely to say “good afternoon” or “good evening” to a family member, friend or even colleague when you see them later in the day; the generic hi, hello or even the more modern and youthful hey is
In French, these expressions at different times of the day can translate variously into either greetings or farewells. On rising, you wouldn’t say “bon matin” (“good morning”) when you open your eyes to your bed-mate or stroll into your local boulangerie to pick up your morning baguette: you would say simply bonjour — or, more politely, bonjour madame/monsieur in the latter case. The only time you might use bon matin is in the expression de bon matin, which means “bright and early”*. The same is true for “good afternoon”: the French don’t use bon après-midi as a greeting at the start of the afternoon; rather, it’s a farewell when you’re waving someone off or parting company after le dejeuner. Bonne soirée is another more time-specific version of au revoir (“goodbye”), when you’re kissing both cheeks as the afternoon draws to a close, or wishing your cherie a pleasant evening as she heads out with her friends.
Bonsoir is multi-functional: it’s the evening equivalent of either bonjour or au revoir, and it’s the only one of these time-specific words or expressions that is appropriate on both meeting and parting — in this case after about 6pm, when the evening lies ahead, together or apart. Bonne nuit (“good night”) is the final farewell of the French day, as night falls, lovers part, families and friends retire for the night, and dreams and passions beckon.
The standard French greeting at any time of day is bonjour (with the accompanying kiss on each cheek); salut is a more casual hello if you bump into a friend outside or the meeting is fleeting or unexpected. There is a French equivalent of the American service farewell “have a nice day”: bonne journée is bidden by shop-keepers, waiters, ferrymen …
Both au revoir and adieu mean goodbye — they translate literally as “to the seeing again” and “to God”. Au revoir is the more usual and casual — equivalent to “see you later”, or at least suggesting a rendezvous in the near future. Adieu is goodbye, more formal, poignant, grave or poetic; it’s more likely to be said if you don’t know how long the separation might be, or if a certain finality is implied or desired.
*In Québec, bon matin can be used as an informal greeting between close friends and long-time colleagues. As I understand it, French-speaking Canadians and Swiss both have variations on all the above; examples and comments are welcome.