Modals of speculations help us express a guess about something. We choose the verb depending on how sure we are of that particular guess.
As we know, the modals of speculation are the following: must, might, may, could and can’t. How do we use each one of them?
- Must: We use must when we know 100% that something that we are saying is true.
You were not scared. You must be a very brave person. (we use must here because we know for a fact that this person is very brave)
I can’t believe you have been waiting all this time! You must be really bored.
- Might/may/could: we use might, may or could if we think that something is possible but we are not sure. There is a 50% chance that it is true.
We may arrive late if the traffic is really bad.
I would take an umbrella if I were you. It looks like it might rain.
In a few years it could be too late.
(In all those situations you don’t really know if it is true or not, but It is a possibility)
- Can’t: We use can’t if we know for sure 100% that something isn’t true.
That can’t be John, he at home right now.
(In this example, we know 100% that it is not John)
IMPORTANT: When we are speculating we don’t use mustn’t, can or couldn’t. We can use might not and may not.
