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I have seen that to talk about some past events by using modals,we mostly use perfect modals(such as could have ,should have, would have, might have ,may have)and to talk about future and present events, we mostly use normal modals. However I also know that most modals have the same form for past, present and even future. I mean that we should be able to use perfect modals even for future , especially using some time words ,such as "by the time" ,"by tomorrow" ,"by next month". but however, on some sites (like this ) ,I saw someone asking a question similar to mine,and he was answered that he must not use perfect modal for future, even though the sentence includes "by the year" , "by tomorrow", and the other these type words. for example:

you must complete the work by tomorrow

as you can see normal modal (To me ,"must have completed", "need to have completed",and "should have completed" fit more perfectly to the sentence above compared to normal modals)

Overall I am asking if we can (and should) use perfect modals for future events (probably near future) if we use the time words (adverbs) that are for future perfect tense.

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  • It's would have, should have, must have, might have + Past Participle.
    – Lambie
    Commented Jul 15 at 15:16

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if we use the time words (adverbs) that are for future perfect tense.

This doesn't really make sense, because no adverbs are normally associated specifically with the "future perfect tense".

I am asking if we can (and should) use perfect modals for future events (probably near future)

You can use a perfect modal if the meaning is appropriate, i.e., if some past action is meant. For example:

  1. By Monday, the stock market might increase by 100 points.
  2. By Monday, the stock market might have increased by 100 points.

The first sentence looks forward from the present time, while the second looks backward from Monday. The meanings are similar.

  1. On Monday, my wife will say that we should buy more stock.
  2. On Monday, my wife will say that we should have bought more stock.

The first sentence looks forward from Monday, while the second looks backward from Monday. The meanings are different.

Also, keep in mind that two modal verbs ("will" and less frequently "shall") are closely associated with the future and future perfect tenses. For example:

By Monday, the stock market will have increased by 100 points.

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  • Really?,I don't know, somehow we can say :you need to have completed the task by the end of this month,(and also have to have completed) but must, may ,should have completed don't works here ? .
    – DARK DRAGON
    Commented Jun 9, 2022 at 12:50
  • @DARKDRAGON "You must / may / should have completed the task by the end of this month" are all correct. For example: "Eurystheus says that Hercules must have finished cleaning the stables by the end of this month."
    – MarcInManhattan
    Commented Jun 9, 2022 at 14:39
  • So , overall "must ,should ,may might have done" can be used as "will have done" ( as finished action in the future )
    – DARK DRAGON
    Commented Jun 9, 2022 at 19:01
  • So this is correct, by the end of this year(start of 2023),I might have completed learning English.(might shows that I'm not quite sure I will have completed learning by the end of this year.)
    – DARK DRAGON
    Commented Jun 9, 2022 at 19:23
  • @DARKDRAGON Yes, that's right.
    – MarcInManhattan
    Commented Jun 10, 2022 at 4:22

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