I'm wondering whether this is grammatically correct?

I'll do something when I have done something else

have done something else hasn't happened and will be some time in the future

closed as off-topic by Lawrence, Kris, choster, Hellion, J. Taylor Feb 7 at 12:20

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  • I suggest it could be clearer to say: "I'll do something after I have done something else" – Kim Ryan Feb 2 at 3:18
  • This question may be migrated to English Language Learners It's a valid question but is better on the other sister site. – Kris Feb 2 at 9:19

The verb have done in present perfect tense means that the action is in the past and it is implied that it has some consequences in the present. There are other tenses that are the ones used for events that have not happened yet, or that could/would happen, or for events that are happening but not finished.

The verb will do in future tense is strictly in the future.

That makes the sentence as correct as I will do something yesterday, which is structurally sound, but the meaning is paradoxical.

Note how the fix that you were given in the comments, I'll do something after I have done something else, resolves the paradox with the exchange of when and after. With when an event in the past is claimed to be simultaneous with one in the future, with after then past and future are in the right order.

  • What didn't you like? – lei Feb 2 at 5:14
  • 2
    "I'll come with you when I have finished my tea" is perfectly idiomatic to me, whether or not it is strictly grammatical. – Kate Bunting Feb 2 at 9:00
  • @KateBunting Why doubt its grammaticality? – Kris Feb 2 at 9:18
  • When can mean (just) after: 2. after which; and just then (implying suddenness). "he had just drifted off to sleep when the phone rang" en.oxforddictionaries.com/definition/when – Kris Feb 2 at 9:22
  • @Kris I was wondering whether pedants would say it should be 'when I will have finished'. – Kate Bunting Feb 2 at 9:24

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