word usage - Special use of 'might' and 'could'

Special use of might and could¹ [58]

i You were mad to drive so fast: you might/could have been killed.
ii We could/might be in Africa. [knowingly uttered in France] (Perhaps somewhere long abandoned in the south of France. I add this. Correct me if I'm wrong.)

These do not fall into either of the above major categories: there is no implicit condition, but the preterite conveys much more than a slight element of tentativeness.

In [i] the (circumstantial) possibility existed but was not actualised: you weren’t killed.

[ii] can also be regarded as unactualised circumstantial possibility, but differs from [i] in that there is no element of cause and effect (as your being killed was a possible result of your driving so fast); it can be glossed as “It is as though we were in Africa — we’re not, but judging from appearances there's no reason why we should not be”.

I'm more interested in the application of case [ii].

1. 
   

   Suppose I am eating an ice-cream cone, and it tastes like caviar, can I say "I could/might be eating caviar."? (Apparently I'm not)

   
   


2. 
   

   Suppose I forgot my laptop's password, but my sister somehow inadvertently got it cracked, can I say to my sister "You are so smart. You could/might be a Russian hacker."? (Apparently she's not)

   
   


3. 
   
   

   Suppose I'm watching Luis Suarez biting his Italian opponent, can I say to my sister "Suarez could/might be a cannibal. Don't be a fan of his."? (Apparently he's not)

   
   

Would my remarks correspond with the context?

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^{1. Page 201, The Cambridge Grammar of the English Language, aka CGEL.}

Answer

From my experience, might and could can both be used in situations as you've described above, but carry different meanings. In U.S. English, the two words have different connotations, so using one or the other subtly changes the meaning and intent of the sentence.

Let's use your hacker example. (I'm only using one example since they're all basically the same.)

Suppose I forgot my laptop's password, but my sister somehow inadvertently got it cracked, can I say to my sister "You are so smart. You could/might be a Russian hacker."

Could is used when something is possible, but probably not currently true. If you say "You could be a hacker", you are suggesting that your sister has the skills to be a hacker, but you don't actually believe that she is one.

Might is used when something is possible, and the evidence leads you to believe in that possibility. If you say "You might be a hacker", then you are saying that your sister is so good at computers, you think there is actually a chance she ...might be a hacker. (Or you're saying it ironically, the same as saying "You're so smart! Are you sure you're not a hacker?")

Therefore, in your examples, you would want to use could, and not might.