We use Future Perfect to show that action will be completed before a point in time in the future.
The components for this tense are
- action will happen in the future
- action will be completed before a point in time in the future
A point in time in the future can be:
another action
I will have done my lessons before my brother comes
We don’t use future tenses after
before, after, when (if “when” is equal to “by the time when”), by the time, if
That is why we used Present Simple “before my brother comes“
However, the first part is in the Future Perfect: “I will have done”
Let’s reverse the same sentence:
After I have done my lessons, my brother will come
In the above example, we didn’t use Future Perfect for the same reasons. We don’t use future tenses after “after.” That is why instead of Future Perfect, we used its counterpart from the present tenses – Present Perfect.
time on clock
I will have done my lessons by 3 pm.
event
I will have done my lessons before the exam.
date
I will have done my lessons by the 1st of October.
contextual time (not explicitly indicated, however, we can understand it from context)
Contextual time: Future Perfect
Contextual time can be any time point (another action, time on clock, event, date) that we can infer from the situation (context).
(question) How will you pass the exam?
(answer) I will have done my lessons. (point in time is not explicitly indicated)
Here, contextual time is “before the exam.” It falls into event category. Just to make sure we are using Future Perfect correctly, we can convert this sentence:
I will have done my lessons before the exam.
As you can see, the above example circles back to the previous one.
Simple way to explain Future Perfect
Well, another way to explain Future Perfect, not that scientific, however, closer to our human nature, is:
When something is completed in the future before something else. The action that is earlier, out of the 2 actions, will be in Future Perfect.