The concept is elusive: in the future, you will have done something in the past?

Question

Maybe you could describe a situation to which this would apply?  I recall the play, "La guerre de Troies n'aura pas lieu," but that was a triumph of imagination.  When would you work this into everyday conversation?

Accepted Answer

Hi Susan, the future perfect is used for describing a future (hypothetical) event that is in the past relative to another future event. So both events are in the future, but one is in the past with respect to the other.
For example, "There's a detour, so I can't stop by John's tonight, because I will have driven home a different way." or "By the time I wake up I'll have only had 4 hours sleep!"
It's quite common to have to use it. I hope that helps!

Answer

Helps a lot.  I can relate especially to, "By the time I wake up I'll have only had 4 hours sleep."
Merci!