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Hi

I'd like to ask you about can/might.

There's the sentence: They can/might be away for the weekend but I'm not sure. I know the answer should be "might," but why "can" is incorrect? How about "could"?

Another sentence: He can/could be French, judging by his accent. I know the answer should be "could," but why "can" is incorrect? How about "may" or "might"?

One more: You can/might be right but I'm going back to check anyway. I know it should be "might," why not "can"? How about "could" or "may"?

thanks
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I guess this is an unofficial reply.

These sentences are all conditional. They might not be away for the weekend. He might not be French. You might not be right.

When you can do something the statement isn't conditional. There may in fact be conditions, but they would have to be stated elsewhere. They're not part of this statement or this sentence.

I can have your car running for you in ten minutes.
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might and could have more doubt than can and could, when used in present time

May/might means possibilty
They might be away for the weekend but I'm not sure: the doubt about the possibility is in your mind. Can/could isn't really recommended here, because you're not talking about their capability of leaving for the weekend, but about the doubts/possibilities in your mind.

Can/could mean capability (be able to)
Now, make your choices again:-)
IMO, only:
He may/might be French, judging by his accent

is correct.
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Comments  
The words used to show possibility are might, may, and could. Not can. can means have the ability to. You are not interested in saying that they have the ability to be away for the weekend. You are not interested in saying that he has the ability to be French. You are not interested in saying that someone has the ability to be right. What you are interested in saying is that there is a possibility that they are away for the weekend, a possibility that he is French, or a possibility that someone is right.
<> See Modals.
CJ
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Thank you for your clarifications guys, they were helpful!