I wonder if someone could help with a grammar debate a couple of ESL teacher friends and I are having. This is a multiple choice question from an IELTS test.

He ________ gone to work yesterday. John was there all day and nobody saw him.

  1. mustn't have
  2. wasn't have
  3. can't have

Source: PDF file p2, Q34

The correct answer to the blank according to the test was "can't have" gone. One American ESL teacher disagrees, saying that answer is incorrect, and should read "couldn't have" gone (which wasn't a possible answer).

I have two questions.

  • Which of these two modal phrases (not sure if that's the correct grammar term) is proper;

  • I believe the second sentence is saying that "nobody saw John" and doesn't refer at all to the subject of the first sentence, where my friend believes the second sentence means "nobody saw the subject of the first sentence, and John didn't see the subject of the first sentence either", on the basis that the first sentence gives context to the second. Which is the correct reading?

Also, my friend teaching ESL thinks that "can't have gone" is technically correct, as any given phrase should have only one past tense element, excluding passive voice, which uses V3 (past participle) in every tense. He also thinks that "couldn't have gone" is a valid answer because of it being in common use, and was not included as an option in order to avoid confusion.

  • 1
    What makes you think there's only one answer? – Hot Licks Mar 17 '18 at 21:28
  • @HotLicks That was the IELTs instructions. I'm fine with there being more than one answer. – calligraphic-io Mar 17 '18 at 21:33
  • @personallearner I guess I've not understood the exact difference between "can" and "could". I can use both to express a future action: "I can go to the store after work", "I could go to the store after work". With "can", it seems to me to be expressing simple ability, i.e. I have the time / transportation / etc. to go to the store. The variant with "could" seems to me to express a "hedging", like "it's possible, I don't really want to". But neither are in the past, as your comment suggests? If I want to use "could", I need to use a perfect form I think: "I could have gone to the store"? – calligraphic-io Mar 17 '18 at 21:36
  • The choice between the two would be something of a judgment call, and depend on the details of the impediment. "Can't" would be more apt to be used if, say, the speaker actually saw the individual somewhere else. "Couldn't" would probably be preferred if the speaker knew that the individual was scheduled to be somewhere else. (But none of this really fits with the following sentence. Are we talking about John or someone else?) – Hot Licks Mar 17 '18 at 21:47
  • 4
    If it was a multiple-choice test then presumably there were options given. What were they? (Please edit those into the question) – Andrew Leach Mar 17 '18 at 22:04

The "he" in the first sentence must refer to a different person, let's call him "Bob", presumably "Bob" and John work in the same office. Yesterday John went to work but Bob didn't. John didn't see Bob "him" (him) and neither did anyone else at work. Ergo...

He (Bob) can't have/couldn't have gone to work yesterday [because] John was there all day and nobody saw him (Bob) [at work].

The only answer possible from the multiple choice is No.3. “can't have”.

We use must / may / might / can't / couldn't + have + past participle to make deductions and speculations about the past; can't have tells us the speaker is sure something didn't happen or that a situation is impossible. Could have is also possible.


From the Cambridge Dictionary's page dedicated to the modal verb “can”

Guessing and predicting: can’t as the negative of must

When we want to guess or predict something, we use can’t as the negative form of must. We use can’t have + -ed form as the negative form of must have + -ed. Can’t and can’t have + -ed form express strong possibility:

A: Roy must have made a lot of money.

B: He can’t have done. He doesn’t even own a house. (A makes a deduction that Roy has made a lot of money. B sees this as very unlikely and so expresses it as a negative possibility.)

On p394 in Practical English Usage (edition 1991) by Michael Swan:

Must is used with the perfect infinitive for deductions about the past.

  • "The lights have gone out" -- "A fuse must have blown."
  • "We went to Majorca." -- "That must have been nice."

[emphasis mine]

Must is only used in this way in affirmative sentences. In questions and negatives, we use can and can't instead.

Thus the opposite of “That must have been nice” is “That can't have been nice”

  • Apart from the grammatical considerations, there is also a contextual one. What John did or did not do is speculation. Now, the choices have been changed, and in no case is "wasn't have" right and "mustn't have" is quasi-obsolete. With the three new choices, it can only and obviously be: can't have, in terms of the "list". – Lambie Mar 18 '18 at 17:04
  • @Lambie the choices haven't been changed, the OP was always asking about "can't have" vs. "couldn't have", he forgot or didn't think that the multiple choice had to be listed. You've seen the edit, there's nothing to prevent you from improving your answer further still. I didn't explain why "wasn't have" is wrong, but why "mustn't have" is. – Mari-Lou A Mar 18 '18 at 17:14
  • "Wasn't have" is a grammar mistake. The other two at least exist. I like the must/can't have point. – Lambie Mar 18 '18 at 17:19
  • @Mari-LouA Thank you for the work on your answer. I'll accept an answer soon, the question came from two friends / ESL teachers and we agreed to have consensus on the answer to accept. It's all of our first experience with the site. – calligraphic-io Mar 18 '18 at 22:55

I must start by declaring an attitude. In my view, multiple choice language questions are often flawed, above all in relation to English. Their alleged merit, simple objective marking over subjective marking, is often a deceptive illusion.

Such is the case here. There are two tests of grammaticality: whether the utterance is understandable and whether it sounds odd in some way.

both the “can’t have” and the “couldn’t have gone to work yesterday” make sense, given an appropriate reason, and neither comes across as in any way odd.

“He can’t have gone to work in the City of London yesterday, because (I say over my mobile) I am waiting for him to collect his bags here in Tokyo airport at 6:30 in the morning.”

“He couldn’t have gone to work yesterday, because he was with me all day in Paris.

This raises another question: whether there are rules or norms about when can and when could must be preferred. Perhaps there is a rule of time or mode. I shall have to research more about that.

One consideration is that the two are negated differently. I can reply to “he couldn’t have gone”, “Oh yes he could: I saw him there myself.”. Try the same with ‘can’t have’. “Oh yes he can have” sounds wrong. Why? Pause for thought and grandchildren.

  • Thanks Tuffy! I want to share the various answers with the other people I mentioned were discussing this before voting for an answer. Can you explain how you would research the rule of time or mode? I am pretty limited to reading Wikipedia articles on grammar issues, I don't know where else to look. – calligraphic-io Mar 17 '18 at 23:59
  • @calligraphic-io I shall start with the Oxford English Grammar (OUP 1996). We are dealing with usage here. There is a history to grammar as well as to lexicography. There had been a steady change over time as to WHOSE use of the language sets the ‘standard’. Increasingly the mass public becomes influential, along with journalism. Further back it would have been literary texts. But there is then another group of authorities: school text book publishers and exam boards (including IELTS!). Also, we are dealing with lack of grammar teaching in many schools from the ‘60s through the ‘80s. – Tuffy Mar 18 '18 at 8:34
  • Re. recent edit. Because "can't have" is used to express disbelief at statement in the past tense; e.g. A: He went to the Fijis yesterday B: He can't have. I saw him this morning. – Mari-Lou A Mar 18 '18 at 9:48

Here are most -[if not all] of the grammatical choices for this:

He ________ gone to work yesterday. John was there all day and nobody saw him.

  • can't have [meaning: It is just not possible that he went]
  • may not have [meaning: he possibly did not go]
  • couldn't have [meaning: past conditional, stronger than can't have]
  • might not have [and the variation: mightn't have, mostly UK]
  • should have gone [this is actually possible here, though it may be argued that one needs a "but" here heading the next sentence].

Frankly, I see no reason for any of those not being grammatical. I am putting them here just to show what I think are possible as they would not fit easily and be readable in a comment.

  • But for most of those (if not all), "John was there..." is a non-sequitur. – Hot Licks Mar 17 '18 at 22:48
  • No, I don't think that is so. But I am not going to write out an argument for each, I'm afraid. – Lambie Mar 17 '18 at 22:49
  • How odd that several comments see no connexion between the two sentences! To me the second is the explanation for the first, the "he" being the subject of the first sentence. To make that clearer you could create a single sentence with a semi-colon rather than the two sentences with a stop. – JeremyC Mar 17 '18 at 23:05
  • There is a connection but the logic is not the single logic implied by the exam givers. – Lambie Mar 17 '18 at 23:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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