• A: I was surprised that Sarah wasn’t at the meeting.
B: She might not have known about it. ( = perhaps she didn’t know)
• A: I wonder why Colin was in such a bad mod yesterday.
B: He may not have been feeling well. ( = perhaps ha wasn’t feeling well).
Sometimes could has a similar meaning to may and might:
• The phone is ringing. It could be Tim. ( = it may / might be Tim)
• You could have left your bag in the shop. ( = you may / might have left it…) But couldn’t (negative) is different from may not and might not. Compare:
• She was too far away, she couldn’t have seen you. (= it is not possible that she saw you)
• A: I wonder why she didn’t say hello.
B: She might not have seen you. (perhaps she didn’t see you; perhaps she did) We also use may and might to talk about possible actions or happenings in the future:
• I haven’t decided yet where to spend my holidays. I may go to Ireland. (= I will go to Ireland)
• Take an umbrella with you when you go out. It might rain later. ( = perhaps it will rain)
• The bus doesn’t always come on time. We might have to wait a few minutes. (=
perhaps we will have to wait)
We may draw a distinction between the expression of possibility in this way (which allows for speculation and guessing) and deduction based on evidence. Deduction, often expressed with must be and can’t be, suggests near-certainty:
• Jane’s light is on. She must be at home. She can’t be out.
For the past we use must have (done) and can’t have (done). Study this example:
George is outside his friends’ house. He has rung the door bell three times but nobody has answered. They must have gone out. (otherwise they would have answered).
• The phone rang but I didn’t hear it. I must have been asleep.
• I’ve lost one of my gloves. I must have dropped it somewhere.
• Jane walked past me without speaking. She can’t have seen me.
• Tom walked straight into a wall. Ha can’t have been looking where he was walking Study the structure:
5. The use of modals to express advisability, duty/obligation and necessity Study these examples:
(I am obliged to stop smoking and I shall: it is my duty)
(I was obliged to stop smoking and I did: it was my duty)
Advisability necessity: a scale of choice:
We can use modals and other verbs to express advisability on a scale which reflects a degree of choice. This scale may vary according to the subjective point of view of the speaker.
Advisability should: Generally means ‘in my opinion, it is advisable to’ or ‘it is (your) duty’.
ought to: can be slightly stronger than should in that it is sometimes used to refer to regulations or duties imposed from the outside: You ought to vote (= it is your public duty). Should is more likely in questions and negatives.
had better: i s stronger than should and ought to. It is used to recommend future action on a particular occasion, not in general. It carries a hint of threat, warning or urgency.
In the speaker’s opinion there is no choice at all.
The use of ‘must’ , ‘have to’ and ‘have got to’
We use must and have to to say that it is necessary to do something. Sometimes it doesn’t matter which you use because as far as meaning is concerned these three forms are
‘You must do something’ = ‘I (the speaker) say it is necessary’:
• She’s a really nice person. You must meet her. (= I say this is necessary)
• I haven’t phoned Ann for ages. I must phone her tonight.
Compare:
• I must get up early tomorrow. There are a lot of things I want to do.
Have to/have got to is impersonal. We use have to/have got to for facts, not for our personal feelings.
‘You have to/I’ve got to do something’
because of a rule or the situation:
•You can’t turn right here. You have to/have got to turn left. (because of the traffic system)
•My eyesight isn’t very good. I have to wear/have got to glasses for reading.
•George can’t come with us this evening.
He has to/has got to work.
I have to get/I’ve got to up early tomorrow.
I’ going away and my train leaves at 7.30.
‘Need’ as a modal:
Need has only some of the characteristics of modal verbs in that it occurs in:
• Questions: Need you go? Need you leave so soon? (= surely not/ I hope not)
• Negatives: You needn’t go.
In Yes/No question a negative answer is expected. Yes/No question with need? Can be answered with must or needn’t:
• Need I type this letter again? – Yes, you must. /No, you needn’t.
Need + have + past participle behaves in the same way:
• Need you have told him about my plans?
• You needn’t have told him about my plans.
Yes/No question with Need … have …? can be answered: Yes, I had to. (no choice) No, I needn’t have. (I had a choice)
6. The use of modals to express lack of necessity, inadvisability, prohibition
Examples of modal forms to express lack of necessity, inadvisability and prohibition:
Present lack of necessity You needn’t go there
Or: You don’t need to go there.
You don’t have to go there.
Or: You didn’t need to go there.
(= There was no necessity to go there,
You ought not to have parked here.
Lack of necessity can be expressed by needn’t, don’t have to and the more informal haven’t got to (where got is often stressed)
‘You needn’t do something’ = it is not necessary that you do it, you don’t need to do it:
• You can come with me if you like but you needn’t come if you don’t want to. ( =it is not necessary for you to come)
• We’ve got plenty of time. We needn’t hurry.
Needn’t and don’t need to are similar to don’t have to.
• We’ve got plenty of time. We don’t have to hurry.
Needn’t have done: George had to go out. He thought it was going to rain so he took the umbrella. But it didn’t rain, so the umbrella was not necessary. So:
• He needn’t have taken the umbrella.
Compare needn’t (do) and needn’t have (done):
• That shirt isn’t dirty. You needn’t wash it. (present lack of necessity)
• Why did you wash that shirt? It wasn’t dirty. You needn’t have washed it. (you washed it unnecessarily)
inadvisability prohibition: a scale of choice:
We can use modals and other verbs to express inadvisability and prohibition on a scale which reflects a degree of choice. This scale may vary according to the subjective point of view of the speaker.
Inadvisability shouldn’t: Generally means ‘in my opinion, it is inadvisable to’ or ‘it is your duty not to’.
oughtn’t to: can be slightly stronger than shouldn’t. It is sometimes used to refer to regulations and duties imposed from the outside:
You oughtn’t to park so near the crossing. (= it is your public duty not to do this).
had better not: is stronger than shouldn’t and oughtn’t to. It is used to recommend future action on a particular occasion, not in general. It carries a hint of threat, warning or urgency. You’d better not overtake here.
am/is/are not to: can be used for instructions: You are not to park here.
can’t is nearly as strong as mustn’t to suggest something is prohibited.
You can’t park here.
mustn’t: conveys absolute prohibition. In the opinion of the speaker, there is no choice at all. This opinion may be subjective or may be supported by some outside authority as in You must turn left. (e.g. there is a road sign forbidding it) is an alternative to must.
prohibition
Don’t have to and haven’t got to can never replace mustn’t to convey prohibition . Like needn’t, they convey lack of necessity.
Mustn’t conveys the strongest possible opinion of the speaker;
• You really mustn’t say things like that in front of your mother.
• Julian mustn’t hitchhike to Turkey on his own.
Prohibition reflecting external authority (in e.g. public notices , documents) is often expressed as must not (in full):
• Life belts must not be removed.
• Candidates must not attempt more than four questions.
Inadvisability/prohibition can be expressed by: shouldn’t/oughtn’t to/ mustn’t, etc
• You shouldn’t / oughtn’t to / mustn’t / can’t be late for meetings (present)
• You shouldn’t / oughtn’t to / mustn’t / can’t be / had better not be late tomorrow.
(future)
Shouldn’t , oughtn’t to , mustn’t , can’t be , had better not are used to refer to the future although they do not have future forms.
‘Shouldn’t have’ and ‘oughtn’t to have’: Both these forms suggest a criticism of an action:
• You shouldn’t have / oughtn’t to have paid the plumber in advance.
or failure to observe a prohibition
• You shouldn’t have / oughtn’t to have stopped on the motorway.
Exercises
Exercise 1: Complete the sentences using can or (be) able to. Use can if possible; otherwise