Usage of Could
Could itself indicates ability or possibility, often used to refer to the past, but can also refer to the present, where it typically indicates a hypothetical situation or serves as a polite form of can. ❶ Indicates ability. For example: Could I help you? (A more polite way to ask than Can I help you?) Amy couldn’t come yesterday because she was ill. Brandon could speak his native dialect before, but he has forgotten almost all about it now. They said they could swim. ❷ Indicates permission. For example: Could I help you? (A more polite way to ask than Can I help you?) Anthony asked if he could smoke in the hall. ❸ Indicates possibility. For example: Brian said he couldn’t agree any more. Could it be Henry? 可能是亨利吗?
—I’ve taken someone else’s green sweater by mistake. —It ____ Harry’s. He always wears green. A. has to be B. will be C. mustn’t be D. could be 【Answer: D】This question tests the usage of modal verbs. Among the four options, could indicates speculation. Mustn’t indicates prohibition; has to indicates necessity; will indicates certainty when speculating, which is too strong.
❹ Indicates surprise or doubt. When the modal verb could indicates surprise or doubt, could and can can be interchangeable, but using could is more polite. For example: Where could Joyce be now? Carl couldn’t be over sixty.
—I heard they went skiing in the mountains last winter. —It ____ true because there was little snow there. A. may not be B. won’t be C. couldn’t be D. mustn’t be 【Answer: C】Based on the provided context, there was little snow, indicating that the claim of skiing in the mountains is unlikely to be true. Couldn’t be true expresses the speaker’s doubt and surprise about the skiing situation, meaning: it can’t be true.
❺ Used in hypothetical sentences. For example: I would go if I could. If the door were unlocked, the house could be robbed. If you had worked harder, you could have succeeded.
If I ____ plan to do anything I wanted to, I’d like to go to Tibet and travel through as much of it as possible. A. would B. could C. had to D. ought to 【Answer: B】This question tests the usage of modal verbs. The meaning is: If I could do whatever I wanted, I would like to go to Tibet and explore as much of it as possible. This indicates that the author emphasizes a possibility.
