The modal auxiliary could is used in several very different
ways. One happens when sentences with can are used in
indirect (reported) speech and the main verb is past.
Examples:
Bill said, "Can you help me, Carol?" ----->
Bill asked Carol if she could help him.
Carol replied, "I can't now, but I can later." ----->
Carol replied that she couldn't help Bill then
but added that she could help him later.
Lucy said, "Can you speak Thai, Dave?" ----->
Lucy asked Dave if he could speak Thai.
Dave replied, "I can understand it better than
I can speak it. ----->
Dave answered that he could understand Thai
better than he could speak it.
Bobby: "Can I have some dessert, Mom?" ----->
Bobby asked his mother if he could have
some dessert.
Bobby's mother said, "No, you can't, Bobby,
because you haven't finished your vegetables. ----->
Bobby's mother told him that he couldn't have
any dessert because he hadn't finished his vegetables.
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Special Notes:
1. |
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The time for can is still present or future in the
indirect-speech sentences above. In the sentences,
can changes to could "artificially" because the
main verb is past. |
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2. |
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In an indirect-speech speech sentence, it's possible
not to change the verb after can if it refers to
something that is in general time:
Dave said, "I can understand Thai better than
I can speak it. -----> Dave said that he can
understand Thai better than he can speak it.
(The sentence is also correct with could.)
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3. |
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The negative of could in sentences such as
the sentences above is couldn't (or could not). |
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