by 2050, time travel .... possible.

a) will be

b) will have been

which answer is correct? is it wrong to use "will be" in that case?

  • Why would it be wrong? Can you compose a sentence in which “will have been” would be right?
    – Xanne
    May 17, 2019 at 8:34
  • "Will have been possible" assumes that at some future time it no longer is possible. You might find a contrived sentence where it would work. Otherwise a) is right. If your're a language learner, you'll probably find the ELL site more helpful.
    – S Conroy
    May 17, 2019 at 14:22

2 Answers 2


"Will have" is future perfect tense and refers to something in the future that has been completed, but you want to refer to something (time travel) that will be ongoing in the future, so you need future progressive.

Therefore, 'a' is correct, at least grammatically:

By 2050 time travel will be possible.

You would use "will have been" if you were referring to something completed that allows for the future possibility, for example:

By 2050 the time machine will have been invented.

or simply:

By 2050 time travel will have been made possible.


Best to start by identifying if the verb describes a state or an action. If a state, then it is likely that you wish to show that the state will exist at this point, and continue to exist further into the future.

state verbs, eg believe / prefer / be

By 2050 people will believe that all diseases are curable. NOT: will have believed

By 2050 most people will prefer a vegetarian diet NOT: will have preferred

By 2050 time travel will be possible NOT: will have been

If an action, then a phrase beginning 'by + time/day/date', is more likely to employ a future perfect to show its completion no later than the specified time.

action verbs: close / disappear

By 2050 some species will have disappeared NOT: will disappear

By 5pm that shop will have closed NOT: will close

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