Can I use "would" to signify uncertainty or expectation? And how is that any different from using "might" or "could"? Could all of the below examples be uttered in the present tense? If yes, then how do I know when to use which one since "would", "might" and "could" all signify uncertainty?

1a) The train would be here in 5 mins.

1b) The train might/could be here in 5 mins.

2a) That would appear like a zebra.

2b) That might/could appear like a zebra.

3a) That would be John, go and open the door.

3b) That could/might be John, go and open the door.

What are the nuances between these sentences?


3 Answers 3


According to the Cambridge Dictionary, would can have the following meanings: Future, Intention, Possibility, Request, Willingness, Frequency, Opinion, Advise, Reason, Probability. Please refer to the dictionary for more detailed explanation and examples.

Uncertainty does sound like probability, but expectation does not match anything in the list.

The train would be here in 5 mins - incorrect

You (and probably others) expect that the train will be here in five minutes: that is not a valid usage of would. See my note below about why you can't use would to express probability in a situation like this. AstralBee has offered a good explanation of could and should in this sentence.

That would appear to be a Zebra

This is a set phrase for politely expressing an opinion.

That would be John, go and open the door.

This refers to a probability- the person who has just knocked on door is probably John. Note that we generally use this form to refer to something that is happening now, or has already happened, not something that will happen in the future, so we can't use it to talk about the train arriving in five minutes.

  • How is this different from "That "could" be John..."? Commented Nov 30, 2021 at 18:08
  • 1
    @English--moreexcthanlaws With "could", John might be there, and he might not. The speaker is not committing to either possibility. With "would", the speaker believes that John actually is there; perhaps not 100% but certainly more than 50%. Commented Nov 30, 2021 at 18:26
  • so, what is the differnece between "will" and "would": "That would/will be John"
    – LE123
    Commented Feb 7, 2023 at 8:55
  • @LEHANH as I said in my answer, "That would be..." is a polite way of expressing opinion. "That will be..." is more like stating a fact: it does not acknowledge the possiblility that you might be wrong.
    – JavaLatte
    Commented Feb 8, 2023 at 8:01
  • "That will be..." is more like stating a fact. --> But I think "It is John" is actually a fact.
    – LE123
    Commented Feb 8, 2023 at 15:54

Short answer - no. 'Would' is not used to express expectation or uncertainty. Your examples ask about 'would' and 'could', but the word I think you are missing is 'should'.

  • 'Would' is for indicating future conditionals (or in other contexts, past trends)
  • 'Could' indicates possibility
  • 'Should' indicates expectation.

So, 'The train could arrive in 5 minutes' would mean that it is possible it will arrive then. It doesn't necessarily indicate 'uncertainty', but neither is it a definite time.

'The train would arrive in 5 minutes' is missing a conditional clause. For example, you might say "the train would arrive in 5 minutes, but all the trains are running late".

As you are asking about expectation, I think you need 'should'.

Eg. "The train should be here in 5 minutes".

It doesn't express 'uncertainty' by default - but you can certainly say it with conviction, or uncertainty. Tone of voice would indicate the difference.


"Would" is used as a definite statement, e.g. Polly would be coming means that you are 100% sure about the statement, e.g. that Polly is coming. "Could" and "might" are used for uncertainty, e.g. David might have a pencil means that you are not completely sure about the statement, e.g. if David has a pencil.

  • I think for something definite I'd use " Polly is coming" rather than "Polly would be coming" Commented Nov 30, 2021 at 18:09
  • Though someone may choose one over another, which is perfectly fine, both are completely valid :) Commented Nov 30, 2021 at 18:11
  • How would you explain "If only they would help"? That seems to me to express desire, not certainty. Commented Nov 30, 2021 at 18:14
  • The set phrase for expressing something that is nearly 100% certain is "That would be...", and you only use it about things that happened recently or are happening now. You can't convey the same meaning with "Polly would be..." - it doesn't start with that, and it's talking about something happening in the future.
    – JavaLatte
    Commented Dec 8, 2021 at 11:47

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