English Grammar

Modal verbs are can (could), may (might), must, have to, shall (should, will (would), dare (dared), need (needed), ought to and so on. Modal verbs have no person or number; they cannot be used alone, but must be formed into predicates with the original form of the verb that follows them

I. can, could

1) Express ability (physical strength, knowledge, skill).

Can you lift this heavy box?(Physical)

Mary can speak three languages.(Knowledge)

Can you skate? past tense; whereas be able to has more tenses.

I'll not be able to come this afternoon.

Be able to, not Can, is used when it means "to make an effort to do something successfully". e.g.

He was able to go to the party yesterday. was able to go to the party yesterday evening in spite of the heavy rain.

2) Express request and permission.

-----Can I go now?

----- Yes, you can. / No, you can't.

This can be interchanged with may.

---- Could I come to see you tomorrow?

---- Yes, you can. ( No, I'm afraid not. )

3) To express the objective possibility (the ability to be formed by objective causes).

They've changed the timetable, so we can go by bus instead.

This hall can hold 500 people at least.

4) Expresses speculation (surprise, doubt, disbelief).

This hall can hold 500 people at least.

Can this be true?

This can't be done by him.

How can this be true? It is more euphemistic than may, and is not in the past tense. The negative answer can be can't

or mustn't, which means "can't, forbidden".

----Might/ May I smoke in this room?

---- No, you mustn't.

---- May/Might I take this book out of the room?

--- Yes, you can. - Yes, you can. (No, you can't / mustn't. )

With May I...? is more formal and polite when asking for permission, whereas Can I...? is more common in spoken language.

2) It is used in imperative sentences to express wishes.

May you succeed!

3) To express speculation, possibility (not used in interrogative sentences).

Might is not a past tense, and it is less likely than may.

1. He may /might be very busy now.

2. Your mother may /might not know the truth.

3. must, have to

1) Expresses must, necessary.

You must come in time.

When answering an elicited question, if it's negative, you can't use mustn't (禁止，不准), but needn't, don't have to (不必).

---- Must we hand in our exercise books today?

---- Yes, you must.

---- No, you don't have to / you needn'

2) Must is the speaker's subjective opinion, while have to emphasizes the objective need. must is only in the general present tense, have to has more tenses.

1. he play isn't interesting, I really must go now.

2. I had to work when I was your age.

3) To express speculation, possibility (only used in affirmative declarative sentences)

1. You're Tom's good friend, so you must know what he likes best.

2. Your mother must be waiting for you now.

Four,

2. Your mother must be waiting for you now.

4. dare, need

1) dare as modal verb, often used in question, negative and conditional clauses, the past tense form is dared.

1. How dare you say I'm unfair?

2. He daren He daren't speak English before such a crowd, dare he?

3. If we dared not go there that day, we couldn't get the beautiful flowers.

2) need as a modal verb is often used in questions and negative sentences.

2) need as a modal verb is often used in questions and negative sentences. In affirmative sentences, it is usually replaced by must, have to, ought to, should.

1. You needn't come so early.

2. ---- Need I finish the work today?

---- Yes, you must. / No, you needn't.

3) When dare and need are used as substantive verbs, there are changes in person, tense and number. In affirmative sentences, dare is often followed by the infinitive with to. In questions and negative sentences, dare can be followed by the infinitive with or without to. But need can only be followed by an infinitive with to.

1. I dare to swim across this river.

2. He doesn't dare (to) answer.

3. He needs to finish his homework today.

5.

What shall we do this evening?

2) shall is used in the second and third person to indicate that the speaker is giving the other person an order, warning, promise or threat.

1. You shall fail if you don't work hard.(warning)

2. He shall have the book when I finish it.(promise)

3. He shall be punished.( threat)

4. Threats)

6. will, would

1) To express requests, suggestions, etc., would is more euphemistic.

Will / Would you pass me the ball, please?

2) Expresses will, desire and determination.

1. I will never do that again.

2. They asked him if he would go abroad.

3) would denotes an action or a tendency that has occurred repeatedly in the past. "

3) would denote an action or a tendency that has occurred repeatedly in the past.

1. During the vacation, he would visit me every other day.

2. The wound would not heal.

4) Expresses estimation and conjecture.

It would be about ten o'clock when she left home.

7. should, ought to

1) should, ought to express "ought to".

1) should, ought to express "should" and "ought to" express obligation or responsibility, which is heavier than should.

1. I should help her because she is in trouble.

2. You ought to take care of the baby.

2) Expressing advice, suggestion and order. should, ought to can be used in general, but commonly used in question sentences.

1. You should / ought to go to class right away.

2. Should I open the window?

3) Express speculation

should , ought to (objective speculation), must (subjective speculation). should , ought to (objective speculation), must (subjective speculation).

1. He must be home by now. (断定他已到家)

2.He ought to/should be home by now.(不太肯定)

3.This is where the oil must be.(直爽)

4. This is where the oil ought to/should be.(直爽)

4. This is where the oil ought to/should be.(implicit)

VIII. Modal verbs + infinitive perfect (have done)

1) can / could + have done in affirmative sentences means "could have done but can actually do something".

1) can / could + have done in affirmative sentence means "could have done but actually can do something", it is virtual voice; in question or negative sentence means doubt or uncertainty about the past behavior, expresses speculation.

1. You could have done better, but you didn't try your best. (virtual voice)

2. He can't have been to that town. p>3. Can he have got the book?(Presume)

2) may / might + infinitive perfect (have done)

It expresses a presumption about past behavior. It can't be used in interrogative sentences, and there is no use of the virtual voice. might expresses a lesser possibility than may.

1. He may not have finished the work .

1. He may not have finished the work .

2. If we had taken the other road, we might have arrived earlier.

3) must + infinitive perfect (have done)

Used in affirmative sentences to express speculation about past behavior. It means "must, think". Its questionable, negative form is replaced by can, can't. See 1) can / could + have done to express presumption.

1. You must have seen the film Titanic.

2. He must have been to Shanghai.

4) should + infinitive perfect (have done)

Used in affirmative sentences to express speculation about past behavior.

He should have finished the work by now.

It means that "something should have been done, but it wasn't."

The negative of this expression means that a certain kind of behavior shouldn't have happened, but it did.

It can be interchanged with the infinitive to have done.

1. You ought to / should have helped him. (but you didn't.)

2. She shouldn't have taken away my measuring tape, for I wanted to use it. She shouldn't have taken away my measuring tape, for I wanted to use it.

5) needn't + infinitive perfect (have done)

It means "something was actually done when it didn't have to be done".

You needn't have watered the flowers, for it is going to rain.

6) will + infinitive perfect (have done)

Mainly used in the second and third person, it expresses a presumption that an action or a state of affairs has already been accomplished. The main purpose of the infinitive is to express a presumption about an action or state of affairs that has been accomplished.

He will have arrived by now.

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