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What is the difference between might have and could have?

He might have come. He might have studied.

He could have come. He could have studied.

How would you describe a possibility? For example:

It's possible that he came from a different culture.

It's possible that he come from a different cutlure.

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@FumbleFingers. Not a possible duplicate. – Noah Apr 16 '12 at 4:44
I still think it is. The only issue here is that in current usage could associates with capability as well as with possibility, whereas might only associates with the latter. Granted, the only existing answer on the earlier question doesn't fully cover the issue, but I'd rather see that one polished up that another one created. For your purposes, the short answer here is both your first two sentences are equivalent, and both your last two are questionable/invalid because of verb tenses. – FumbleFingers Apr 16 '12 at 15:48

Could and might are often, but not always, interchangeable. He might have come / studied = 'We don’t know whether has come / studied or not', but you could substitute could. If you want to indicate ability or permission, however, you need He could have come / studied = ‘He had the ability to come / study.'

It's possible that he came from a different culture would be used in considering a historical figure who didn’t seem to fit into his environment. If you were talking about a current situation, you’d say It's possible that he comes from a different culture. It’s hard to think of any circumstances in which It's possible that he come from a different culture would be used, even if you regard ‘come’ as subjunctive.

English modal verbs are both important and subtle. You're unlikely to gain a full understanding of their use in exchanges such as this and if, as I assume, Noah, you are a non-native speaker of English you really need the help of a qualified English teacher.

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+1, good answer to a question (or two questions, really) that's difficult to answer. – Amos M. Carpenter Apr 16 '12 at 8:50
It would be really good if you'd post a version of this answer again the dup I linked to. There's only one answer there at the moment, and it's not actually very good, so you'd be practically bound to get some kind of badge for reviving something so old. More to the point, I'm getting a bit tired of seeing variants of this issue come up again and again - we could seriously do with a canonical answer to close them against. – FumbleFingers Apr 16 '12 at 15:52
@FumbleFingers: Kind of you to suggest it, but I fear it’s beyond my modest powers to explain in any answer here what grammar books take several pages to explain, and even then not always comprehensively. Those who look for a quick fix will do so in vain. – Barrie England Apr 16 '12 at 16:55
Yeah - I quite agree the whole area gets complex in the details. Not to mention the passage of time - only my opinion, but for example I think over the decades & centuries, "may/might" has shifted away from ability towards likelihood, while "can/could" has gone in the opposite direction. But then there's "will/would", "shall/should", etc. Arrrgh! – FumbleFingers Apr 16 '12 at 17:32

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