When I write something about the past, what form of must should I use? For example, can I say,

She must finish that yesterday.

or should I say,

She might finish that yesterday.

? I feel that the word might is too weak.

  • 'Might' doesn't mean the same thing as 'must' anyway; it expresses possibility, not obligation. Commented Apr 26, 2018 at 8:30
  • It's also weird that you end your sentence on yesterday, you would expect it to have finished now so you would have "[...] have finished that yesterday."
    – JJJ
    Commented Apr 26, 2018 at 19:03

1 Answer 1


Neither of those examples work because the way the word must is used implies something that will be done, not something that was done. There are, however, some alternatives.

She's not busy today. In order for her to have this free time, she must have finished her homework yesterday.

Or, without using the word must but something that means the same thing:

She had to finish her homework yesterday in order to enjoy her free time today.

Actually, if you're writing a fantasy or science fiction story, one where time travel is possible, then your sentences could actually make sense.

In such a scenario, "she must finish that yesterday" could be taken to mean "she must travel back in time to yesterday and finish it."

But outside of that possibility, you would need to rephrase it.

  • If she finished it yesterday use 'She had to finish ... . ' If she did not finish but was supposed to finish yesterday use: 'She should have finished ... .' Also, in this present case 'She must have finished' cannot be used by the person who is/was supposed to finish. In this context it could be used by another person who is wondering or asking whether she finished yesterday or not.
    – JoHKa
    Commented Apr 26, 2018 at 5:00

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