MODAL VERBS – MODAL PERFECT: Ñoäng töø khieám khuyeát – Khieám khuyeát hoaøn thaønh)
A. Modal Verbs: (Ñoäng töø khieám khuyeát) laø caùc ñoäng töø maø sau chuùng ta duøng ñoäng töø nguyeân maãu khoâng TO:

1. Can (coù theå chæ moät khaû naêng): Chæ coù 2 hình thöùc hieän taïi ñôn (CAN) vaø quaù khöù ñôn (COULD). Do ñoù muoán söû duïng nghóa coù theå ôû caùc thì khaùc ta phaûi duøng BE ABLE TO ñeå thay theá nhöng CAN laïi dieãn taû moät khaû naêng chaéc chaén hôn BE ABLE TO

          Eg.    Can you speak any foreign languages?

                   Are you able to speak any foreign languages?

2. Could and was/were able to: Thænh thoaûng COULD laø quaù khöù cuûa CAN, nhöng chuùng ta duøng COULD ñaëc bieät vôùi caùc ñoäng töø: see, hear, smell, taste, feel, remember, understand.

          Eg. When we went into the house, we could smell burning.

* Ngoaøi ra chuùng ta coøn söû duïng COULD ñeå noùi ai ñoù coù moät khaû naêng ñaëc bieät:

          Eg. My grandfather could speak five languages.

* WAS / WERE ABLE TO: duøng ñeå dieãn ñaït moät tình huoáng ñaëc bieät ñaït ñöôïc (manage)

          Eg. They didn’t want to go with us at first but in the end we were able to persuade them.

* COULDN’T: ñöôïc duøng trong baát kyø tình huoáng naøo.

          Eg.    My grandfather couldn’t swim.

                   We tried hard but we couldn’t persuade them to come with us

3. Must – Inf. (aét haún): tieân ñoaùn moät söï vieäc xaûy ra ôû hieän taïi vaø theå phuû ñònh cuûa noù laø Can’t Inf.

          Eg. He must be tired. ® He can’t be tired (not "Mustn’t”)

* Must – Inf. (phaûi) = have to nhöng have to Inf. Coù nghóa baét buoät hôn. Vaø theå phuû ñònh cuûa Must laø khoâng caàn (needn’t)

4. May / might – Inf. (Coù lẽ, coù theåõ) duøng ñeå dieãn ta moät söï suy ñoaùn gaàn ñuùng.

          Eg.    He may be in his office (= Perhaps he is in his office)

                   He might be having lunch. (Perhaps he is having lunch.)

* May – Inf. Coøn dieãn taû moät söï xin pheùp. Nhöng might coù theå ñöôïc duøng trong caâu ñieàu kieän loaïi 1.

Eg.    May I go out?

                   If the weather is fine, we might go for a picnic.

* May / might: ñöôïc duøng ñeå noùi veà moät söï vieäc hoaëc haønh ñoäng coù theå xaûy ra trong töông lai:

          Eg. I’m not sure where to go for my holidays but I may go to Italy. (= Perhaps I’ll go)

            The weather forecast is not very good. It might rain this afternoon. (Perhaps it’ll rain)

* Theå phuû ñònh laø May not hoaëc might not (mightn’t)

5. Must. Mustn’t, Needn’t:

a. Must: caàn thieát phaûi laøm

          You haven’t got much time. You must hurry.

b. Mustn’t: caàn thieát do ñoù khoâng ñöôïc laøm

          You can tell Tom what I said but he mustn’t tell anybody else.

(= It is necessary that he doesn’t tell anybody else)

c. Needn’t – Inf.: = don’t / doesn’t need to: Khoâng caàn

          You have got plenty of time. You don’t need to hurry (You needn’t hurry)

B. Modal Perfect (ñoäng töø khieám khuyeát hoaøn thaønh) laø ñoäng töø khieám khuyeát coù HAVE + P.P theo sau .Ta coù caùc Modal Perfect sau ñaây:

1.     Could have + P.P: raát coù theå ñaõ (dieãn taû 1 khaû naêng ñaõ coù trong quaù khöù, nhöng chöa ñöôïc söû duïng tôùi).

2.     Couldn’t have + P.P: Taát nhieân ñaõ khoâng theå (dieãn taû 1 haønh ñoäng hieån nhieân khoâng theå laøm ñöôïc)

3.     Should have + P.P: Ñaùng leõ phaûi (dieãn taû 1 lôøi khieån traùch ñoái vôùi 1 haønh ñoäng quaù khöù ñaùng leõ neân laøm maø laïi khoâng laøm)

4.     Shouldn’t have + P.P: Leõ ra khoâng neân (dieãn taû 1 lôøi khieån traùch ñoái vôùi 1 haønh ñoäng quaù khöù ñaùng leõ khoâng neân laøm maø laïi laøm).

5.     Must have + P.P: AÉt haún ñaõ (dieãn taû 1 söï suy ñoaùn gaàn ñuùng veà 1 söï kieän ôû quaù khöù:

6.     Can’t have + P.P: Coù leõ ñaõ khoâng (dieãn taû 1 söï suy ñoaùn khoâng chaéc chaén veà 1 söï kieän ôû quaù khöù)

7.     May/ might (not)  have P.P: Coù theå, coù leõ (dieãn taû nhöõng gì coù theå (hoaëc khoâng) xaûy ra ôû quaù khöù)

8.     Needn’t have P.P: Khoâng caàn bieát( Dieãn taû moät söï vieäc khoâng caàn thieát phaûi bieát roõ söï vieäc hoaëc thôøi gian)

9.     Would have + P.P: Coù leõ ñaõ (duøng trong caâu ñieàu kieän loaïi 3)