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?
Best Answer
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.
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.
This is a set phrase for politely expressing an opinion.
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.