Future Perfect and Future Continuous with present reference

Question

I came across this dialogue:

• Is it too late to call them? Do you think they'll have gone to bed yet?

• Knowing them, they won't have finished their dinner yet. They'll be watching a film.

My question is why are the future perfect and the future continuous used in these sentences?

I couldn't find any reliable information. In the case of the future continuous it might be "future as a matter of course", but I'm not sure and have absolutely no ideas as to the future perfect here.

I'd be grateful for any ideas.

Answer 1

The second speaker's will does not signify futurity; it is an epistemic use, marking the clause as the speaker's confident inference of probability from knowledge of the subject and the circumstances.

A: Hey, Bob isn't in his office. I need to ask him about this script.
B: Oh, he'll be at lunch now. I can give you his cell number if it's an emergency.

The first speaker's will could be understood as a future ("Do think it probable that if we call them we will find they have already gone to bed"), but should probably be understood as another epistemic ("Do you think it probable that they are already in bed?").

Answer 2

It is used to express something that has been done before the moment of the actual conversation

Answer 3

Since the call has not been made yet, "When I/you call them" is implied in the subsequent statements.

For example: "When you call then, they'll be watching a film." is correct usage of the future continuous.

As for use of future perfect, this is due to the negation.

In practice, "they will not have finished their dinner yet" (perfect) is merely a different way of saying "they will still be eating dinner" (continuous). Perfect tense becomes necessary in this particular case because the emphasis is on an action's completion, it's just that the speaker is saying the completion will not have occurred.