Phân biệt cách sử dụng can, could và (be) able to

PHÂN BIỆT CÁCH SỬ DỤNG CAN, 
COULD VÀ (BE) ABLE TO 
A. Chúng ta sử dụng can để nói rằng một điều gì đó là có thể hoặc ai đó có khả 
năng làm việc gì đó. 
Chúng ta sử dụng can + infinitive (can do / can see etc.): 
- We can see the lake from our bedroom window. 
- Can you speak any foreign languages? 
- I can come and see you tomorrow if you like. 
Phủ định là can't (= cannot): 
- I'm afraid I can't come to the party on Friday. 
B. (Be) able to  có thể được dùng thay cho can, nhưng can vẫn thông dụng hơn: 
- Are you able to speak any foreign languages? 
Nhưng can chỉ có hai dạng thức, can (present) và could (past). Đôi khi cần phải sử 
dụng (be) able to . So sánh: 
- I can't sleep. 
nhưng 
- I haven't been able to sleep recently. (can không sử dụng được với thì hiện tại 
hoàn thành) 
- Tom can come tomorrow. 
but 
- Tom might be able to come tomorrow. (can không có dạng nguyên mẫu) 
C. Could và was able to  
Đôi khi could là quá khứ của can. Chúng ta sử dụng could đặc biệt với: 
see hear smell taste feel remember understand 
- When we went into the house, we could smell burning. 
- She spoke in a very low voice, but I could understand what she said. 
 Chúng ta cũng sử dụng could để nói rằng ai đó có khả năng hoặc được phép làm gì 
đó: 
- My grandfather could speak five languages. 
- We were completely free. We could do what we wanted. (= we were allowed to 
do ) 
Chúng ta sử dụng could để nói về những năng lực chung chung. Nhưng nếu chúng 
ta đang nói về những gì đã xảy ra trong một tình huống cụ thể, chúng ta sử dụng 
was/were able to  hoặc managed to  (không dùng could): 
- The fire spread through the building quickly but everybody was able to escape. 
hoặc  everybody managed to escape. (không nói could escape) 
They didn't want to come with us at first but we managed to persuade them. 
hoặc  we were able to persuade them. (không nói could persuade) 
So sánh: 
- Jack was an excellent tennis player. He could beat anybody. (= he had the 
general ability to beat anybody) 
 nhưng 
- Jack and Alf had a game of tennis yesterday. Alf played very well but in the end 
Jack managed to beat him. hoặc  was able to beat him. (= he managed to beat 
him in this particular game) 
Phủ định của could làcouldn't (could not): 
- My grandfather couldn't swim. 
- We tried hard but we couldn't persuade them to come with us. 
- Alf played well but he couldn't beat Jack.