Future perfect
Relatively rare in English, the future perfect serves to express one future action which precedes a future moment or another future action. Moreover, it asserts that these actions will be completed before the principal action. It is formed by adding the modal "will" to the auxiliary "have," preceding thepast participle:
- She will have finished before eight o'clock.
- Tomorrow morning they will all have left.
- They will already have finished eating by the time we get there.
One can often use the simple future instead of the future perfect, but a nuance is lost: the simple future does not emphasize the completion of the first action:
- Tomorrow morning they will all leave. (The future perfect would emphasize that they will already have departed before tomorrow morning.)
- They will finish eating by the time we get there. (They may finish just as we arrive; the future perfect would emphasize that they will have finished beforewe arrive.)
FORM Future Perfect Continuous with "Will"
[will have been + present participle]
Examples:
- You will have been waiting for more than two hours when her plane finally arrives.
- Will you have been waiting for more than two hours when her plane finally arrives?
- You will not have been waiting for more than two hours when her plane finally arrives.
FORM Future Perfect Continuous with "Be Going To"
[am/is/are + going to have been + present participle]
Examples:
- You are going to have been waiting for more than two hours when her plane finally arrives.
- Are you going to have been waiting for more than two hours when her plane finally arrives?
- You are not going to have been waiting for more than two hours when her plane finally arrives.
NOTE: It is possible to use either "will" or "be going to" to create the Future Perfect Continuous with little or no difference in meaning.
USE 1 Duration Before Something in the Future
We use the Future Perfect Continuous to show that something will continue up until a particular event or time in the future. "For five minutes," "for two weeks," and "since Friday" are all durations which can be used with the Future Perfect Continuous.
Examples:
- They will have been talking for over an hour by the time Thomas arrives.
- She is going to have been working at that company for three years when it finally closes.
- James will have been teaching at the university for more than a year by the time he leaves for Asia.
- How long will you have been studying when you graduate?
- We are going to have been driving for over three days straight when we get to Anchorage.
- A: When you finish your English course, will you have been living in New Zealand for over a year?
B: No, I will not have been living here that long.
USE 2 Cause of Something in the Future
Using the Future Perfect Continuous before another action in the future is a good way to show cause and effect.
Examples:
- Jason will be tired when he gets home because he will have been jogging for over an hour.
- Claudia's English will be perfect when she returns to Germany because she is going to have been studying English in the United States for over two years.
Future Continuous vs. Future Perfect Continuous
If you do not include a duration such as "for five minutes," "for two weeks" or "since Friday," many English speakers choose to use the Future Continuous rather than the Future Perfect Continuous. Be careful because this can change the meaning of the sentence. Future Continuous emphasizes interrupted actions, whereas Future Perfect Continuous emphasizes a duration of time before something in the future. Study the examples below to understand the difference.
Examples:
- He will be tired because he will be exercising so hard.
This sentence emphasizes that he will be tired because he will be exercising at that exact moment in the future. - He will be tired because he will have been exercising so hard.
This sentence emphasizes that he will be tired because he will have been exercising for a period of time. It is possible that he will still be exercising at that moment OR that he will just have finished.
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