meaning of the future perfect tense

21:49 May 2, 2011 

... rather than probability. But can it also signify either regret or a wish to soften the impact of what one is saying? Or is the following only expressing a lack of evidence for something the speaker is, nonetheless, convinced about.

Unfortunately, you will have missed him as he will have caught the 6 pm train.

21:28 May 2, 2011 

I think they're all probabilities/hunches/ etc. "This will have been built by the Romans" means "This was probably built by the Romans but I don't have any direct evidence." A more convincing argument would be: "Tacitus said in xxx that this was built during the time of Emperor yyy". No future perfect there - could be complete nonsense of course but the speaker is not expressing uncertainty!

21:12 May 2, 2011 

I'm still not convinced by the "probability" argument - because you can say something like "The train will definitely have left by now" - my hunch is that it is more about reporting something of which you don't have direct evidence, so you say "This will have been built by the Romans" or "He will have been given this by his grandmother" about something which you know to be true but in which you haven't been directly and personally involved.

20:36 May 2, 2011 

He will have left by now = I expect he has left by now.
He must have left by now = In all probability he has left by now (otherwise he'll be late/he always leaves on time/nobody could have left it this late to leave)

19:22 May 2, 2011 

This is not an example of the future perfect. It is also, as Armorel notes, not just about probability. To take up her example "invariably they will have been forced ...": what this really means is that the writer is certain that is the case, not all instances/cases have been substantiated with evidence, possibly because they have not yet all been investigated, but when they are this will be found to be the case, possibly (but not necessarily) because new cases are still occuring. In the Asker's example new cases would still be occuring.

18:59 May 2, 2011 

Here "will" is used as a modal verb with a past meaning, like "must/could/may/might + have + past participle". The modal "will" expresses in this context a high degree of certaintly related to some past action. (...were forced...)

18:22 May 2, 2011 

... and it leaves me trying to define the difference (which is subtle) between "often they have been forced ...." and "often they will have been forced ....". I don't think it's just to do with probability, because you could say "... invariably they will have been forced ..." (i.e. it is always the case - no element of "perhaps").