Modals of Ability
1Công thức
can/could + base verb; be able to (other tenses and infinitive); could + have + past participle (unused past ability)2Giải thích
Can diễn tả khả năng ở hiện tại, could diễn tả khả năng chung trong quá khứ, còn be able to dùng ở các thì khác và dạng nguyên mẫu. Với một thành tích cụ thể trong quá khứ dùng was/were able to hoặc managed to, không dùng could.
Can expresses present or general ability, could expresses past general ability, and be able to is used where can has no form (infinitive, perfect tenses, future). Could have + past participle describes something a person was capable of but did not do.
3Khi nào dùng
- Present and general ability (can)
- Past general ability (could)
- Ability in other tenses (be able to)
- Unused past opportunity (could have + past participle)
4Quy tắc cần nhớ
- For one specific achievement in the past use was/were able to or managed to, not could
- Can has no infinitive or perfect form, so use be able to
- Modals are followed by the bare infinitive and have the same form for all persons
5Ví dụ
My cousin can speak four languages.
When I was ten, I could run a kilometre without stopping.
I haven't been able to sleep properly this week.
6Lỗi thường gặp
- Yesterday I could finish the report in one hour. (single occasion: I was able to / managed to finish)
- I will can join you next week. (I will be able to)
- She can to swim. (can swim)