There are some situations in which one would like to vary the modal verb in counterfactual conditionals, but it seems to be incorrect.

  1. "If things were otherwise, she would keep her promise." This seems like perfectly ordinary usage.

  2. "If things were otherwise, she might keep her promise." This also sounds fine.

  3. "If things were otherwise, she must keep her promise." This sounds wrong. But there is an obvious alternative: "If things were otherwise, she would have to keep her promise."

  4. "If things were otherwise, she should keep her promise." This also sounds kind of bad. But I can't think of an alternative way to convey this thought without bending over backwards. (Maybe "If things were otherwise, she ought to keep her promise," sounds better, but the issue seems to be the same. And "ought" often sounds too formal to my ear.)

My specific question is: Is sentence 4 necessarily incorrect? And if so, is there a better way to convey its thought?

More generally: is it ok to vary the modal verbs in counterfactual conditionals, as in examples 3 and 4?

  • 1
    For (4), you can use she would be obligated to keep her promise.. Commented Jul 16, 2021 at 13:15
  • If things were otherwise, she would have to keep her promise.
    – Lambie
    Commented Mar 13, 2022 at 15:51
  • 4 sounds OK, although I'm not sure if it implies probability or obligation. The use of modals is so complex I don't think any linguist would be confident that they understood every case.
    – Stuart F
    Commented Nov 9, 2022 at 1:04
  • All four sentences are idiomatic.
    – TimR
    Commented Jul 6, 2023 at 15:29

1 Answer 1


Briefly, and without repeating commonplace definitions of would and should.

As a consequence of things being otherwise:

She would = the promise is kept

She might = there is a possibility that the promise is kept

She must = tries to use must in subjunctive form, which is not appropriate. See Can I use the word "must" in subjunctive mood?

She would have to = she is compelled to keep it

She should = she is obliged to keep it but there is a possibility she does not

  • Thank you for the reply, but this doesn't clearly answer either of my questions. "tries to use must in subjunctive form, which is not appropriate" comes close to answering, but the link you shared seems to be about an importantly disanalogous grammatical situation.
    – Rick
    Commented Feb 16, 2021 at 18:03
  • 1
    "must" does not have a subjunctive form....
    – Lambie
    Commented Mar 13, 2022 at 15:48
  • There is no "subjunctive form" in English. There are a couple of constructions (untensed that-complement clauses, like He demanded that she obey/*obeys him; and irrealis past usages like Wish you were/*are here) that various people sometimes call "subjunctive", but they don't agree, so it's better to simply not mention the term; it only upsets them. In any event, modals are not subjunctive, though they have meanings that are similar to subjunctives in other languages. Commented Mar 8, 2023 at 18:45
  • @JohnLawler I believe you are too prescriptive on this one. Collins, for example has "The subjunctive was formerly used in English for situations that were improbable or that expressed a wish. It is only rarely used in modern British English. It is, however, found in certain set phrases and in very formal forms of speech and writing.", and EnglishCLub has "The English subjunctive is a special, relatively rare verb form that expresses something desired or imagined.". There are other examples.
    – Anton
    Commented Mar 8, 2023 at 21:42
  • Oh, there was subjunctive in Old English, and in some dialects of Middle English (and maybe some current local dialects -- I wouldn't know). But all there is now in Modern English is a bunch of set phrases and ritual proscriptions. If you want to call them all "subjunctive", no problemo. But it doesn't mean anything; and "subjunctive" in English is not a "form", but an imaginary inflection. Commented Mar 8, 2023 at 22:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.