Introduction - Modal Auxiliary Verbs
Modal Auxiliary Verbs are a very rich area of the English language. They are used with great frequency and with a wide range of meanings.
|would||shall||should /ought to||must||need|
All of them (except for NEED) can express degress of certainty, probability or possibility of an event. But they can also express ideas such as willingness and ability, permission and refusal, obiligation and prohibition, suggestion, necessity, promise and intention.
Modal Verbs expressing certainty, probability or possibility
In order of certainty:
WILL and WON'T are used to predict a future event or action which are seen as certain. The truth or certainty of what is asserted is more or less taken for granted.
- I will see you later.
- His latest book will be out next month.
WILL and WON'T are also used to express what we believe or guess to be true about the present. They indicate an assumption based on our knowledge of people and things, their routine, character and qualities.
- Don't take the meat out of the oven. It won't be ready yet.
MUST is used to assert what we infer or conclude to be the most logical or rational interpretation of a situation or event. As we do not have all the facts, it is less certain than will. The negative form is CAN'T.
- He walked across the Sahara desert! You must be joking!.
- She can't have a ten-year old daughter! She's only twenty-five herself!
SHOULD expresses what may reasonably be expected to happen. Expectation means believing that things are or will be as we want them to be.This use of SHOULD carries the meaning of "if everything goes according to the plan, then something should happen"; therefore it doesn't suggest negative or unpleasant ideas.
- You have worked hard. You should pass the exam.
- If the flight was on time, he should have arrived in Jakarta early this morning.
MAY expresses the possibility that something will happen or is already happening.
- We may go to Spain this year. We haven't decided yet.
- A - "Where's Sandra?" B - "I don't know. She may be having a bath".
MIGHT, like may, expresses possibility, but is more tentative and slightly less certain.
- I might not be back in time for supper, so don't wait for me.
- It might rain. Take your umbrella.
CAN is used to say that something is possible and actually happens.
- It can be expensive to keep a dog (it can be and sometimes is).
We also use CAN to indicate that there is a very real possibility of a future event happening.
- We can stay with Jessica in London (we will be able to stay)
COULD expresses the theoretical possibility of something happening. It is used in a similar way to might.
- It could be expensive to keep a dog (if we had one, it could or it may not be expensive)
It also suggests that something is less likely or that there is some doubt about it.
- We could stay with Jessica in London (it's possible, if she's there)
Could not is not used to express a future possibility. The negative of could is MIGHT NOT.
- It might not be right.
Couldn't has a similar meaning to can't, but only slightly weaker. Compare it to the previous example.
- She couldn't have a ten-year old daughter! She's only twenty-five herself!
OUGHT TO, as well as SHOULD, + HAVE + PAST PARTICIPLE are used to talk about an expectation that something happened, has happened, or will happen.
- If the flight was on time, he should/ought to have arrived in Paris early this morning.
- The builders should/ought to have finished by the end of the week.
Other uses of modal auxiliary verbs
Obligation and Advice: MUST / HAVE TO / SHOULD / OUGHT TO / HAD BETTER
MUST and MUST NOT are used in formal rules and regulations and in warnings. They express strong obligation, the opinion of the speaker and are associated with a more formal, written style. We can also use it to remind ourselves to do something.
- Bookings must be made at least seven days before departure (formal rule)
- You mustn't steal. It's very naughty (strong negative obligation, opinion of the speaker)
- I must phone Steve when I get home. I said I'd call him last night, but I forgot (to remind ourselves to do something)
HAVE TO expresses a general obligation based on a law or rule, or based on the authority of another person.
- Children have to go to school until they're sixteen (It's the law)
DON'T HAVE TO expresses the absence of obligation.
- You don't have to go to England if you want to learn English.
Sometimes we can use either HAVE TO or HAVE GOT TO. But we use HAVE TO with frequency adverbs such as always, never, normally, rarely, sometimes, etc.
- I often have to work at the weekend to get everything done.
With the past simple HAD TO is used especially in questions and negative sentences.
- When did you have to give it back?
- We didn't have to wait too long for an answer
If HAVE is contracted, then we must include GOT. It is often preferred in informal speech.
- The experiment has failed twice before, so it's got to work this time.
- Don't have a late night. We've got to get up early tomorrow.
Sometimes it is possible to find MUST and HAVE TO together. In this case MUST signifies a logical interpretation and HAVE TO an obligation. For a present situation:
- Now John's mother is nearly 90 she must have to be looked after.
For a past situation:
- I don't know where Sarah is. I presume she must have had to go out to meet someone.
We can often use either SHOULD or OUGHT TO to talk about obligations and recommendations, although SHOULD is much more common. They describe a sort of obligation where you have a choice.
- I think you should wear your glasses whenever you feel like watching TV.
- I haven't heard from Evelyn for ages. Do you think I should give her a ring?
- I don't think parents should/ought to give their children sweets
We can use HAD BETTER instead of SHOULD/OUGHT TO, especially in spoken English, to say that we think it is a good idea to do something. We prefer it if we want to express particular urgency and in demands and threats.
- If you are not well, you'd better ask Ann to go instead (good idea to do something)
- There's someone moving about downstairs. We'd better call the police, quickly. (urgency)
The negative form is HAD BETTER NOT. In question forms the subject comes after HAD.
- He'd better not be late again or he'll be in trouble.
- Hadn't we better get a taxi?
Permission: MAY / MIGHT / CAN / COULD
They are used asking for permission, or saying whether we or other people have it. To talk about permission generally, or permission in the past, we use CAN or COULD. MAY is used to ask for and give permission but it sounds very formal.
- Can/Could I borrow your car tonight?
- May I help you?
Ability: CAN / COULD
CAN expresses ability or is used to say what someone knows how to do, or what is possible. The past is expressed by COULD.
- I can speak three languages.
- Thanks to his new glasses, he could make out what was written on the notice.
In these sentences we can also use ABLE TO without any important change of meaning. To express a fulfilled ability on one particular occasion in the past, COULD is not used. Instead, we use WAS ABLE TO or MANAGED TO.
- She was able to survive by clinging onto the wrecked boat.
- The prisoner managed to escape by climbing onto the roof.
There is a useful difference of meaning between COULD and WAS/WERE ABLE TO: the latter form says not only that you could do something (it was possible for you), but also that you did it.
- a) The door was open and he could go into the room.
- b) The door was open and he was able to go into the room.
In sentence a) (COULD) we only know for sure that it was possible; Sentence b) (WAS ABLE) tells us also that he managed to get in, he succeeded in getting in.