MODALS

MUST

Primary and secondary uses of must

a-     He must have prepared (necessity = it's necessary for him to be prepared)

b-     She must believe (deduction = it's possible she believes)

c-     He had to be prepared for anything, even society (past necessity)

d-     She must have believed that he kept it there for study (past deduction)

In its primary use, must refers to "inescapable obligation" and is a "defective verb". This means we can use it to refer only to the present and the future.

They must leave now.

They must leave tomorrow.

If we want to refer to any other time, we have to use a form of have to.

 In its secondary use, must refer to degrees of certainty. In this use it has only two forms:

They must be right (present form).

They must have been right (past or perfect form).

It follows that had to (be) and must have (been) have very different meanings

CAN, COULD

CAN

1- Ability = be capable of, "He can speak English but he can't write it

know how to, very well."

be able to.

2- Permission = be allowed to, "Can I smoke in here?"

be permitted to. "May I smoke in here?"

(Can is less formal than may in this sense)

3- Theoretical possibility (Contrast may = factual possibility)

"Anybody can make mistake".

COULD

1-     Past ability.

"I never could play the banjo"

2-     Present or future permission

"Could I smoke in here?"

3-     Present possibility (theoretical or factual)

"We could go to the concert".

4-     Contingent (not essential) possibility or ability in unreal conditions.

"If we had more money, we could buy a car".

Note: (a) Ability can bring in the implication of willingness (especially in spoken English):

"Can you do me a favour?"

"Could you do me a favour?"

(b) Past permission is sometimes expressed by could:

"This used to be the children's room but they couldn't make a noise there because of the neighbours".

(c) With some perception verbs, can correspond to the progressive aspect with dynamic verbs:

"I can hear footsteps; who's coming?"

MAY AND MIGHT

MAY

1-     Permission = be allowed to (in this sense may is more formal than can. Instead may not or rare mayn't, the stronger mustn't is often used in the negative to express prohibition).

"You may borrow my car if you like."

"You mustn't borrow my car."

"You are not allowed to borrow my car."

"You may not borrow my car."

2-     Possibility (usually factual)

"The road may be blocked."

MIGHT

1-     Permission (rare)

"May I smoke in here?"

2-     Possibility (theoretical or factual)

"We might go to the concert."

SHALL / SHOULD

SHALL

1- Willingness on the part of the speaker in second and third person. Restricted use.

"He shall get his money."

"You shall do exactly as you wish."

2-Intention on the part of the speaker, only in first person.

"We shall let you know our decision."

3- (a) Insistence. Restricted use.

"You shall do as I say."

"He shall be punished."

(b) Legal and quasi-legal injunction

"The vendor shall maintain the equipment in good repair."

Of these meanings it is only the one of intention that is widely used today. "Shall is, on the whole and especially outside Britain, an infrequent auxiliary with restricted use compared with, will, and would; will is generally preferred, except in first person questions.

SHOULD

1-     Obligation and logical necessity (= ought to)

You should do as he says.

They should be at home by now.

2-     "Putative" use after certain expressions e.g.: it is a pity that I am surprised that...

It is odd that you should say this to me.

I am sorry that this should have happened.

3-     Contingent use (first person only and especially British English) in the main clause (= would).

We should / would love to go abroad (if we had the chance)

4-     In rather formal real conditions.

If you could change your mind, please let us know.

WILL / WOULD

WILL

1-     willingness. Used in polite requests.

2-     Intention. Usually contracted ‘ll; mainly first person.

3-     Insistence. Stressed, hence no ‘ll contraction.

4-     Prediction

The similar meanings of other expressions for logical necessity and habitual present. The contracted form ‘ll is common.

v    Specific prediction.

The game will / must / should be finished by now.

v    Timeless prediction

Oil will float / floats on water.

v    Habitual prediction

He'll (always) talk for hours if you give him the chance.

WOULD

1-     Willingness

Would you excuse me?

2-     Insistence

It's your own fault; you would take the baby with you.

3-     Characteristic activity in the past (often probable effect)

Every morning he would go for a long walk ("it was customary")

John would make a mess of it. (Informal = "it was typical")

4-     Contingent use in the main clause of a conditional sentence

He would smoke too much if I didn't stop him.

5-     Probability

That would be his mother.

 Note: Volition with preference is expressed with would rather / sooner:

A: Would you like tea or would you rather have coffee?

B: I think I'd rather have tea.

The expression with sooner is informal.

MUST

1-     Obligation or compulsion in the present tense (=be obliged to, have - got - to); except in reported speech, only had to (not must) is used in the past. There are two negatives:

a-     "not be obliged to": needn't, don't have to;

b-     "be obliged not to": mustn't.

You must be back at 10 o' clock.

2-     (Logical) necessity. Must is not used in sentences with negative or interrogative meanings, can being used instead.

Must can occur in superficially interrogative but answer - assuming sentences.

Mustn't there be another reason for his behaviour?

There must be a mistake but there cannot be a mistake.

OUGHT TO

Obligation; logical necessity or expectation

You ought to start at once.

Note: Ought to is often felt to be awkward in questions involving inversion, and should is preferred. Still is less categorical than ought is had better / best (+ bare infinitive):

A: Must you go?

B: Well, I don't have to, but I think I'd better (go).

THE TENSE OF MODALS

The usual past tense of may denoting permission is could:

Today, we can / may stay the whole afternoon.

Yesterday, we could only stay for a few minutes.

The following modals are not used in the past tense except in reported speech: must, ought to and need . Had to serves as the past of both must and have to:

He must / has to leave now.

He must / had to leave in a hurry yesterday.

THE MODALS AND ASPECT

The perfective and progressive aspects are normally excluded when the modal expresses "ability" or "permission", and also when shall or will express "volition". These are freely used, however, with other meanings.

Possibility:

He may have missed the train.

He may have been visiting his mother.

He can't be swimming all day.

He can't have been working.

Necessity:

He must have left his umbrella on the bus.

I must be dreaming.

You must have been sitting in the sun.

Prediction:

The guests will have arrived by now.

John will still be reading his paper.