In this sentence:
Supposing Jane ______ with us, what would you do?
The available options for filling in that blank were:
- would come
- will come
- has come
- is coming
Could I know which is correct?
TL;DR: Your test-giver probably wants you to select choice #2 “came”, but this is an extremely poorly designed test not only because one could reasonably argue that either of choices #4 and #5 might also work for some speakers and situations, but also because many other completely valid and perfectly common possibilities are unconscionably omitted from your severely limited — and limiting — available choices.
This test is apparently trying to get you to demonstrate your understanding of what sorts of verb tenses, moods, and aspects are allowable in English conditionals.
If I’m right about its purpose, then it is not, in my considered opinion, a very good test of that. Although there are a few obviously wrong answers, more than one possible “right enough” answer may be possible, of which most were alas! not even given you as potential choices. It’s really not a good test at all.
The only general rule for you to keep in mind is that conditionals always have either a present-tense form or else past-tense form in their protasis, meaning their “if” part. This constrains what can come in the apodosis, the “then” part.
You are being force to choose a protasis, and have been given no freedom in the apodosis, which always uses the conditional form would do in your test question. Since the apodosis form is known, only so many possible protasis forms are allowable, most of which were not even provided to you as valid answers.
You haven’t said whether whoever gave the test allows for more than one possible answer, or for no possible answers. One thing that’s certain is that you weren’t given enough different possible answers to choose from if the goal is to test you on how to put the verbs in the two halves together using different tenses, aspects, and moods.
Therefore, although it is by no means the only answer possible, of the limited answers you were rather unfortunately forced to choose from, the best answer is arguably your second choice, came:
That’s because it’s really the same sentence as:
If I wanted to emphasize the hypothetical, I would have chosen a hypothetical-were construct:
If Jane were coming with us, what would you do? (not, alas, a provided choice)
Supposing Jane were coming with us, what would you do? (not, alas, a provided choice)
This is essentially the same as the came case in the simple past, in that the protasis (the “if” part) of the implied conditional is in the past and the apodosis (the “then” part) is in the conditional.
However, one slight difference is how with were coming, that version is also emphasizing the progressive aspect by using an inflection of be with an -ing verb following it, normally analysed as a present participle.
Although I am not one of them, for some people that hypothetical were is more formal or literary than conversational, or is too unreal, so they would just use the simple past in the protasis. They might choose a simple present for the assumptive part:
But that was not among your possible choices, forcing you to use this instead:
That last one (#6) feels wrong(-ish) to me personally, and I wouldn’t likely generate that sentence, but but some people might say it.
It might also be possible to use choice #4, however, which means another possible answer of your allowable choices is this one:
Sentence #6 above with supposing and is coming both together feels a bit funny to me. It seems to have too much “-ing” in it; I also feel that for me at least, there is a mismatch between is coming in the present and would do in the conditional. That’s why I prefer the “if past, then conditional” formulation, no matter whether you use the hypothetical were or the simple past.
Versions of the sentence where the apodosis (again, the “then” part) is no longer in the conditional can also make fine sense, and are less pie-in-the-sky hypotheticals that way. These take a present-tense verb form in the protasis (again, the “if” part). For example:
If Jane comes with us, what will you do? (not, alas, a provided choice)
Supposing Jane comes with us, what will you do? (not, alas, a provided choice)
Notice that in 8 and 9, since the protasis is now in the present, the apodosis most naturally falls into the conditional.
It might also be possible to use your provided choice #4, however, which means another possible answer of your allowable choices could be this one:
That isn’t too terribly bad. Yes, it’s a present has paired with a conditional would, but people do sometimes say things like that.
For some reason I can’t pin down, I don’t much like the supposing – is coming combination. Too much -ing or something If you really want is coming in the apodosis, then there are also possibile ways of using suppose in place of supposing there.
I still think that a present tense (which is what has actually is, even if it is using a past participle with it; that makes it a “present perfect” construction) in the protasis calls for something else in the apodosis:
Suppose Jane has come with us; what will you do? (not, alas, a provided choice)
Suppose Jane comes with us; what will you do? (not, alas, a provided choice)
Suppose Jane were to come with us; what would you do? (not, alas, a provided choice)
Suppose Jane were coming with us; what would you do? (not, alas, a provided choice)
Of those four, the one with comes in the simple present and the one with has come in the present perfect are the least hypothetical, since it’s no longer an “if X were, then Y would” type of conditional. That shift in nuance into the normal present tense might mean the speaker thinks it more likely that Jane will be with us than in the two were cases.
Those four examples given in 11–14 are respectively equivalent to these if–then conditionals:
If Jane has come with us, what will you do? (not, alas, a provided choice)
If Jane comes with us, what will you do? (not, alas, a provided choice)
If Jane were to come with us, what would you do? (not, alas, a provided choice)
If Jane were coming with us; what would you do? (not, alas, a provided choice)
By switching supposing to suppose, you swap one non-tense form (present participle) to another (infinitive). Whether you choose to analyse that infinitive form suppose as an imperative use or a concessive subjunctive one, it is still an untensed verb that shows no time aspect.
I don’t think much of the test you were given. It’s far too limiting. Here again were your choices:
For an example of using deontic would in the protasis, consider this stealth polite request asking Jane to sit down so we can get started:
Recasting those using suppose in the protasis instead of if is possible, which is more in the style of your own original:
It is critically important that you understand this is a completely different use of would, and therefore different rules. In all five of sentences 19–23, that’s a deontic would, not an epistemic one, so the normal rule forbidding would from appearing in the conditional’s protasis does not apply here.
There are other valid modal possibilities and combinations for that sort of request. For example:
Although I have given 25 possible answers, please do not assume that this posting has exhausted all possible approaches to English conditionals. It most definitely has not, for with English just as in another famous language derived from it, “There’s more than one way to do it!” 😇