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The following example is taken from source

A：We saw a police helicopter overhead yesterday morning.

B：Really? They would have been looking for those bank robbers.

The website says that it is an example of usage of would to express an assumption, presumption or expectation in the past.

As this post indicates, the example here does not mean a hypothetical scenario or a past future tense, but a speculation about a past event.

I'm wondering whether the post was correct in explaining such usage. Please share some wisdom!

Only a few grammar books say "would have + past participle" can be used in this way. The following are a couple of the sources I could find, but I don't know whether they are reliable to believe.

Would + perfect. This use of would signals what we expect somebody to do:

John would have scheduled the meeting.

In this case, it tells us that the speaker expected John to schedule the meeting. We do not know if John actually scheduled the meeting.

-- McGraw-Hill's Essential ESL Grammar, for Intermediate & Advanced ESL Students (2008)

and

One of the children offered to help. That would have been Julie. (assumption about the past.)

-- Mastermind Use of English

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  • I think "They will have been looking for those bank robbers." is not correct. Future perfect (will have been) requires a reference time in the future, which is missing in this example.
    – Nico
    Commented Apr 12, 2014 at 17:28
  • I think this link may help you.
    – Nico
    Commented Apr 12, 2014 at 17:32
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    That's not fair. Each of my question concerning "would" refers to different usage of this word, just like seeing a diamond from different aspects!
    – Kinzle B
    Commented Apr 14, 2014 at 13:03
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    @MaulikV sorry. I thought your comment was meant to flag this question as duplicate.
    – Nico
    Commented Apr 14, 2014 at 13:09
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    No, not that deep. I am not a linguist. I have understood nearly the whole picture. This should be my last puzzle piece. Maybe it's also the hardest one since even PEU avoids to include this usage. I am very eager to get a good answer to it. @Maulik V
    – Kinzle B
    Commented Apr 14, 2014 at 13:29

4 Answers 4

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+50

The first thing I would say about modal verbs is that their usage extends over many different contexts and so any general rules are bound to fail when taken out of context.

Outline

  1. Use of 'will' and 'would' to express belief
  2. Other uses
  3. The answer

1. Use of 'will' and 'would' to express belief

(Credit for this section should go to @snailboat)

To illustrate the difference in use of 'will' and 'would' for expressing certainty, snailboat suggested the following sentences at the ELL chat room:

1A. I'm sure they have been looking for those bank robbers.

1B. I'm sure they will have been looking for those bank robbers.

2A. I'm sure they had been looking for those bank robbers.

2B. I'm sure they would have been looking for those bank robbers.

In sentences 1A (they have been) and 2A (they had been) the speaker knows they have/had been looking for those bank robbers. The main difference is that the use of present perfect in 1A (they have been) indicates that the search has lasted at least until now.

In sentences 1B (they will have been) and 2B (they would have been) the speaker expresses a belief:

  • in sentence 1B (they will have been), the speaker expresses the belief that they have been looking for those bank robbers.

  • in sentence 2B (they would have been) the speaker expresses the belief that they had been looking for those bank robbers.

2. Other uses

Again, a word of caution, the interpretation above is not unique and can change if the context changes. This section shows other possible uses of will have been and would have been.

  • To express a hypothesis

    I'm sure they would have been looking for those bank robbers if they had any manpower to spare.

  • To express an event in the future

    They will have been looking for those bank robbers for hours before the CCTV footage is shown on tomorrow morning's News.

3. The answer

Let's now consider the example in your question:

A： We saw a police helicopter yesterday morning.

B： I'm sure they would have been looking for those bank robbers.

To be able to use "will have been" is necessary to change the context as described in the first section of this answer:

A： We have seen a police helicopter.

B： I'm sure they will have been looking for those bank robbers.

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  • Excellent answer. As an aside, if I asked you, "What do you think? Do you want to walk to the concert?" then a perfectly reasonable response would be: "I think we would be late. Let's take a train." Incidentally, this doesn't mean I disagree with what you wrote here – in fact, it's quite the opposite! As you said initially, "their usage extends over many different contexts .. so any general rules are bound to fail" in another context. I would fully agree.
    – J.R. ♦
    Commented Apr 14, 2014 at 14:58
  • @J.R. I started to edit my answer after a chat with snailboat and I ended up rewriting the whole answer. I hope I didn't removed any of the bits you liked.
    – Nico
    Commented Apr 14, 2014 at 17:11
  • Is the sentence "I'm sure they will have been looking for those bank robbers" truly grammatical? I've read that a sentence using the Future Perfect Continuous should mention a point in the future when the action will stop.
    – CowperKettle
    Commented Oct 19, 2014 at 7:44
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    @CopperKettle, how you read the phrase "they will have been looking for ..." depends entirely on the context. In section 2, I've given an example that can be read as what you call "Future Perfect Continuous"; the purpose of section 1, however, was to give an example that expresses belief (the purpose is not to locate an action in the future).
    – Nico
    Commented Oct 22, 2014 at 9:17
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    @KinzleB No, in the OP's example, B isn't pretty sure, B isn't expressing certainty. Note that B starts the sentence with "Really?". B is expressing a belief. B believes that the police had been looking for those bank robbers.
    – Nico
    Commented Oct 2, 2015 at 23:34
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A： We saw a police helicopter overhead yesterday morning.

B： Really? They would have been looking for those bank robbers.

This sounds incorrect to me. Personally, I would say something like "Really? They WERE PROBABLY looking for those bank robbers." In order to use this verb tense here, you would need a situation like...

A: Our police helicopter was supposed to be out looking for those bank robbers yesterday.

B: Really? The helicopter would have been responsible for locating and apprehending them, but I hear the helicopter ran out of fuel right before the call and had to return to base.

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I'm writing this as an answer because it is too long to be a comment, so it's not really an answer to the question; for the answer see Nico's. I'm adding some information that I think will make things a little clearer for the OP.

A: We saw a helicopter yesterday morning .

B: I'm sure they would have been looking for those bank robbers.

Here, would is used as the past of will. So let's look at this as the past of will + infinitive without to. The verb phrase is used to express certainty, which, in a sense, is a certain speculation or an assumption.

The infinitive without to appears to be a perfect one, in a progressive form, i.e. have been looking. This is from the tense of the event (They have been looking for those bank robbers).

Now let's look at the examples you gave.

John would have scheduled the meeting.

One of the children offered to help. // That would have been Julie.

In would + perfect above, we can probably view would as a less definite form of will that is used to express certainty (I take it that you have Practical English Usage; these are under 633.2 and 629.3 respectively.) This, too, can be considered a speculation or an assumption.

The perfect here is used just to show that the event is in the past--at the point before the time of speaking (see this post for extremely thorough detail).

All of the above is how I view all the examples from my understandings; they shouldn't be regarded as authoritative. If anyone finds any mistake in this post, I'll be glad to correct it as soon as possible.

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  • You say I've never seen the more definite form, will + perfect, used this way. Why is that?
    – Kinzle B
    Commented Apr 15, 2014 at 16:17
  • Probably because will + perfect is mainly used to refer to the future, what you may have learnt as the future perfect tense. It may cause confusion if they use it this way. This is the only reason I can think of. If you may excuse, I would say that I see it as just the way they use their language.
    – user1513
    Commented Apr 15, 2014 at 16:21
  • but PEU 629.3 also says "will have +pp" can be used to refer to the past. e.g. We can't go and see them now - they will have gone to bed. However, PEU does not say how often it is used in conversation and in written texts.
    – Kinzle B
    Commented Apr 15, 2014 at 16:31
  • Oh, then that's a mistake on my side. I'm taking that line out. I think it's just that I don't have enough experience; if it were something rare, then PEU would explicitly state so.
    – user1513
    Commented Apr 15, 2014 at 16:34
  • "To express a hypothesis .... I'm sure they would have been looking for those bank robbers if they had any manpower to spare." ... Is the hypothesis in the present?
    – Gamal Thomas
    Commented Nov 13, 2019 at 12:47
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1B is incorrect "I'm sure they will have been looking for those bank robbers"--makes no sense. "I'm sure they will have found those bank robbers by morning. By tomorrow morning, they will have been looking for those robbers for over 20 hours." makes sense. You need a reference of a stopping point in the future.

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  • "I'm sure they will have been..." makes perfect sense. It is quite a common usage.
    – Chenmunka
    Commented Nov 9, 2019 at 10:49

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