Quote:
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Anyone, go ahead, make a sentence using <might> as the past tense of <may>; <should> for <shall>; <would> for <will>; <could> for <can>.
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You
can find examples of "could" being used as a past tense.
EG:
Can you think of an example?
< this can only mean now - it can't mean "in the past". You can't say "can you think of an example yesterday?"
Could you think of an example?
< this can refer to the past. (It might also be used as a polite way of saying "can", but it's the only way to refer to the past.)
I can't think of anything
< there's no way this can refer to the past; it's present only.
I couldn't think of anything
< can refer to the past.
I could have been there (correct)
I can have been there (incorrect)
I don't think that may, shall and will operate in the same way, and I don't want to get involved in a linguistic argument anyway - but there are your can/could sentences.