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?