Hypotheses (things that we imagine)

When we are talking about hypotheses:

• We use present tense forms after phrases like what if, in case and suppose to talk about the future if we think it is likely to happen:

Those steps are dangerous. Suppose someone has an accident.
We should leave home early in case we are late.

• We use a past tense form to talk about the future after suppose and what if to suggest something is not likely to happen:

It might be dangerous. Suppose they got lost.
What if he lost his job. What would happen then?

• We use modals would, could for a hypothesis about the future:

We can’t all stay in a hotel. It would be very expensive.
Drive carefully. You could have an accident.

• We use would in the main clause and the past in a subordinate clause to talk about the imagined future:

I would always help someone who really needed help.
I would always help someone if they really needed it.

• We use modals with have to talk about something that did not happen in the past:

I did not see Mary, or I might have spoken to her.
It’s a pity Jack wasn’t at the party. He would have enjoyed this party.
Why didn’t you ask me. I could have told you the answer.

British Council. (n.d.). Wishes and Hypotheses. Retrieved December 9, 2012, from http://learnenglish.britishcouncil.org/en/english-grammar/verbs/wishes-and-hypotheses