Can we use "would" for expectations/uncertainty?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

"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.