Will have vs must have

Question

Hello, how do you know which translation to English to use? Thank you

Accepted Answer

Hi James, 
This is an interesting question because it is something that cropped up when I was writing some fill-in-the-blank exercises on the futur antérieur.
The translation into English is sometimes 'must have' rather than 'will have' when someone is making assumptions or supposing what might have happened rather than an event that will have happened by the time you do something in the future.
If you take a look at the two different exercises you should see what I mean -
Au retour du travail (Le Futur Antérieur) 
En attendant Aline (Le Futur Antérieur) 
In the first one, a wife is thinking about what her husband and her children will have done by the time she gets home in the evening. In the latter one, parents are wondering what must have happened to their daughter who didn't come home on time.
I would also like to add that we are reviewing the lessons on the future antérieur.
Hope this helps!

Answer

Future perfect tense is always "will have" and not "must have". Maybe you can provide a specific example to show what you mean?

Answer

Above. There are at least three examples where the sentence is translated as “must have”.

Answer

Which translation to use to English ? Whichever and whatever sounds more natural in English in the context and circumstance to reflect the meaning of the French sentence ( that is, your understanding of that meaning ).

This is not a question of French necessarily having different meaning, but English having different expressions to express the same or similar meanings.

Remember, a French speaker is not trying to say something in English with French words, they are saying something in French that a translator tries to match as closely as possible into English/another language.