Must(deduction) compared to may/might

The difference is best seen by examples:

(a) Imagine that we have three keys on a ring and we know that one of these keys opens the cellar door. We might begin by picking one key and saying:

This may/might be the key. (Perhaps this is the key.) But after trying two keys unsuccessfully, we will pick up the third key and say This must be the key. No other choice remains.

(b) / wonder why Tom hasn 't answered my letter. ~ Pie may/might be Hi

(Perhaps he is ill. But there are other possibilities also: he may be

away or too busy to answer.)

But imagine that Bill never has any visitors. If an ambulance stops at his door the neighbours will say Bill must be ill. This is the only possible explanation of the arrival of the ambulance.

(c) Similarly, when considering a past action:

He may have come by tram. (Perhaps he came by train. But there are other possibilities: he might have come by taxi or bus.)

But He must have come by taxi implies that he had no choice. There was

no other way of making this journey.

158 have/had used for deduction

This is an American usage which is sometimes heard in Britain. have/had here is chiefly used with to be:

There's a tall grey bird fishing in the river. ~ It has to be/must

be a heron. had + to be can express the speaker's feeling of certainty in the past:

There was a knock on the door. It had to be Tom. (She was sure it

was Tom.) had + to be can also be an alternative to must + perfect infinitive:

/ wonder who took the money. ~ It had to be Tom/It must have been

Tom. He's the only one who was there.

But, to avoid confusion, the student is advised to stick to the must forms.

159 can't and couldn't used for negative deduction

A Negative deductions about a present event can be expressed by

can't/couldn't with the present infinitive of the verb be or with the continuous infinitive of any verb:

chili): Can I have some sweets? I'm hungry.

MOTHER: You can 't/couldn 't be hungry. You 've just had dinner.

ANN (looking through binoculars): An aeroplane is pulling up people from the boat!

TOM: It can 't/couldn 7 be an aeroplane. It must be a helicopter. He says he's still reading 'The Turn of the Screw'. ~ He can 't/couldn't still be reading it. I lent it to him ages ago and it's quite a short book.

B Negative deductions about a past event are expressed b\

can't/couldn't + the perfect infinitive or continuous perfect infinitive of any verb:

A man answered the phone. 1 suppose it was her husband. ~ It can 't/couldn 't have been her husband. He's been dead for ages.

I took a Circle Line train to St Paul's. ~ You can't/couldn't have

taken the Circle Line. It doesn't go through St Paul's. You must

have been on the Central Line.

couldn't must be used when the deduction is made in the past or introduced by a verb in the past tense:

She said I couldn't have come on the Circle Line.

He said it couldn't be an aeroplane. Otherwise either can't or couldn't can be used.

160 will and should for assumption

A will used for assumptions about present or past actions

will here can be used with the present infinitive (for non- deliberate actions only) or with the continuous or perfect infinitive:

Ring his home number. He'll be at home now. (I'm sure he's

at home.)

He'll be expecting a call from you. (I'm sure he's expecting a call.)

He'll have finished his supper. (I'm sure he has finished his supper.)

It's no use asking Tom; he won't know. (I'm sure he doesn't.)

Will Bill be at the club now, do you think? (Do you think he is?)

B should used for assumptions about present or past actions should here is used mainly with the present infinitive (for non-deliberate actions only) in the affirmative or negative. It is sometimes also possible with the continuous and perfect infinitives:

The plane should be landing now. (I expect it is landing.) The letter should have arrived by now. (I expect it has arrived.) Assumptions with should are less confident than assumptions with will:

Tom should know the address. (I expect Tom knows it.) But Tom'll know the address. (I'm sure Tom knows it.) He should have finished by now. (I expect he has finished.) But He'll have finished by now. (I'm sure he has finished.) should is not used for assumptions which displease the speaker:

Let's not go shopping now. The shops will be very crowded, (should would not be used.)

But for the opposite (agreeable) assumption, either word could be used: Let's go shopping now. The shops will be/should be fairly empty or The shops won't be/shouldn 't be too crowded.

C will and should can also express assumptions about the future: He should/will have plenty of time to get to the station. They shouldn 't/won 't have any difficulty in finding the house.

will + present infinitive used for assumptions about the future is not

restricted to non-deliberate actions. (See also 209.)

D ought to can be used in the same way as should in B and C above:

The plane ought to be/should be taking off in a minute. But should is the more usual form.

16 The auxiliaries dare and used

Dare

A In the affirmative dare is conjugated like an ordinary verb, i.e.

dare/dares in the present, dared in the past. But in the negative and interrogative it can be conjugated either like an ordinary verb or like an auxiliary, i.e. it is a semi-modal. Negative: present do/does not dare dare not

past did not dare dared not

Interrogative: present do you/does he dare? dare you/he?

past did you/did he dare? dared you/he?

The ordinary verb construction is more commonly used.

B Infinitives after dare

Negatives and interrogative forms with do/did are in theory followed by the infinitive with to, but in practice the to is often omitted:

He doesn 't dare (to) say anything.

Did he dare (to) criticize my arrangements? dare I/he/you? etc. and dare not forms take the infinitive without to:

Dare we interrupt? They dared not move. When dare is preceded by nobody, anybody etc. the to is optional:

Nobody dared (to) speak.

C dare is not much used in the affirmative except in the expression I daresay. I daresay (or I dare say) has two idiomatic meanings:

1 'I suppose":

/ daresay there '11 be a restaurant car on the train.

2 'I accept what you say (but it doesn't make any difference)':

english TOURIST: But I drive on the left in England!

SWISS POLICEMAN: / daresay you do, but we drive on the right here.

TRAVELLER: But the watch was given to me; I didn 't buy it. CUSTOMS OFFICER: I daresay you didn't, but you'll have to pay duty on it all the same.

daresay is used in this way with the first person singular only.

D how dare(d) you? how dare(d) he/they? can express indignation: How dare you open my letters? (I am angry with you for opening them.) How dared he complain? (I am indignant because he complained.)

E dare is also an ordinary transitive verb meaning 'challenge' (but only to deeds requiring courage). It is followed by object + full infinitive: mother: Why did you throw that stone through the window? SON: Another boy dared me (to throw it).

162 Used

A Form

used is the past tense of a defective verb which has no present tense.

Affirmative: used for all persons

Negative: used not/usedn't for all persons

Interrogative: used you/he/they? etc.

Negative interrogative: used you not/usedn't you? etc.

Negative and interrogative can also be formed with did:

didn't use to did you use to? didn't you use to? This is a more informal form, common in conversation. used is followed by the full infinitive, and to remind students of this it is often referred to as used to (just as have used for obligation is referred to as have to).

B Use

used is used:

1 To express a discontinued habit or a past situation which contrasts with the present:

/ used to smoke cigarettes; now I smoke a pipe.

He used to drink beer; now he drinks wine.

She usedn 't to like Tom but she quite likes him now or

She used to dislike Tom but she quite likes him now. used is not normally stressed, but it can be stressed if the speaker wishes to emphasize the contrast between past and present.

2 To express a past routine or pattern. Here we are not making a contrast between past and present; we are merely describing someone's routine during a certain period. Very often there is a succession of actions, used to here is replaceable by would (but would cannot replace used to for a discontinued habit etc. as in 1 above), used here is always unstressed.

Tom and Ann were a young married couple. Every morning Tom used to kiss Ann and set off for work. Ann used to stand at the window and wave goodbye. In the evening she used to welcome him home and ask him to tell her about his day.

If we use would we have:

Every morning Tom would kiss Ann and set off for work. Ann would stand at the window and wave goodbye etc.

Remember that used has no present form. So for present habits or

routines we must use the simple present tense.

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