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Suppose you send a message to a person which is not online!

I know

By the time you see this message I will have been done with my task

means that my task is already finished some time before he or she sees the message.

I want to know what is the difference in meaning if I change the second clause to a present perfect:

By the time you see this message I have been done with my task.

Is it grammatical at the first place? This question comes just from my curiosity.

  • Do you understand the usage of "By the time ..." phrases? Since they introduce future actions, only your first example is acceptable. It may help if you simplify your examples from "have been done with my task" to "have finished my task". – user3169 Jun 15 '18 at 6:02
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    A person who is not online ... – Tᴚoɯɐuo Jun 15 '18 at 12:57
  • Try will have completed my task versus have completed my task. – Tᴚoɯɐuo Jun 15 '18 at 12:58
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    In your question it is a single instance. Adding "everyday" changes things, since you really can't have a past to everyday, right? – user3169 Jun 19 '18 at 5:45
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    You must also look at the tensed verb in the clause where by the time is used and determine its time reference. Every day, by the time I get home, the sun has set.. There get refers to a general state of (current) affairs, which is one of the roles of the present tense. But here, By the time I get home tonight, the sun has set, get home tonight refers to the future, and so the present perfect has set cannot be used. By the time I get home tonight the sun will have set. – Tᴚoɯɐuo Jun 19 '18 at 11:06
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The present perfect is not compatible with time-phrases that exclude the present. The phrase by the time you see this message is a reference to the (speaker's) future which excludes the present no less than a reference to the past excludes it.

The correct tense is future perfect, will have been done. By some point in the future, the point when you see this message, my task will have been done (not has been done).

  • I'd appreciate knowing the rationale for the downvote, and being shown an example where a time-phrase that excludes the present is idiomatic in combination with the present perfect. – Tᴚoɯɐuo Jun 15 '18 at 17:39
  • Thanks, my motivation was this example "The sun has already set by the time I get home everyday" from this page: grammar-quizzes.com/8-6.html – Cardinal Jun 19 '18 at 2:35
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    @Cardinal: If you would read my answer again, you will see that the time-phrase in your clause is not simply by the time but by the time you see this message. The verb see refers to the future there. The exclusion of the present is semantic; English has no (morphological) future tense. The same phrase could refer to a general truth or fact, not to the future: By the time you see this poorly placed road sign, you have missed your exit. – Tᴚoɯɐuo Jun 19 '18 at 10:25
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The first sentence is ok. The second one is unappropiate because the second clause should bear an action in the future. I started to do my task at 5 a.m It takes about 2 hours to finish it. You will come home at 7.15 a.m By the time you see this message, I will have finished doing my task.

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To me, none of your two sentences looks perfect. The first sentence, though correct, sounds a little odd and can be changed to either -

By the time you see this message I will be done with my task

or

By the time you see this message I will have done my task

As far as the second sentence is concerned, it doesn't convey anything. The structure is too odd to construe anything meaningful out of it.

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