SUMMARY OF FUNCTIONS OF MODAL VERBS

USE PRESENT/ FUTURE PAST NOTESability/ lack of ability

She can drive a carShe’s able to use a PC.He can’t play the piano

When she was 5, she could / was able to ride a bike.After trying for years, he was able to break the secret code.

Although she tried very hard, she couldn’t/ didn’t manage/wasn’t able to lift the stone off her foot

Here we cannot use “could” as we are talking about a single, past action, not a general ability. We could substitute “was able to “ for “managed to”.BUT - NO difference in meaning when “could” is used in the negative,

possibility He can still be at home (90% certain)She could still be at home (50% certain)Steve may be working late (50% certain )She might be a little late (40% certain; perhaps she will be late)It is likely that they will come with us (90% cettain)David is unlikely to fly to Rome (90% certain that he won’t fly)He is bound to get that job he wants. (95% certain)

We could have been injured, but luckily we weren’t.Mary may have fallen asleep (perhaps she has)Lucy might have tried to contact us (perhaps she has)It was likely that she had missed the last bus.She was unlikely to have missed the last bus.

probability He will be home soon. (100% certain; this is a prediction based on knowledge of the person’s habits)he should pass the test (9’% certain; future only, it’s very probable.They ought be home by now (90% certain they will probably be home in a minute – otherwise, the speaker will be seriously worried.

She should have called by now. (She probably has called)

He ought to have gone to bed by now (he probably has already gone to bed.)

deduction and speculation

She must be tired (90% certain – positive; I’m sure she’s tired)They can’t be rich! (negative; I’m sure they aren’t rich)He couldn’t be at work (negative; I’m certain he isn’t at work)

She must have completed the race.

She can’t have lost her keys again!

They couldn’t have called in to see us!

(Positive; I’m sure she has completed the race)

(negative; I’m sure she hasn’t lost them – I f she has, she’s in trouble!)

(Negative; we were at home all day; I’m sure they didn’t come),

permission You can/ are allowed to go out tonight (giving permission/informal)You can’t have friends over tonight (refusing permission)

I could go out alone when I was a teenager.

I was allowed to go out alone last night (permission for one particular action)

(general permission)

Here it would be incorrect to say “I could go out alone last night” as “could” is only used for

Could I open a window? (Formal, asking permission)You may go out (formal, giving permission)Might I use your laptop) (very formal, asking permission)

I’m afraid you can’t / mustn’t use it (formal; refusing permission)Children under 12 may not enter without an adult (formal refusing permission – written notice)

I couldn’t / wasn’t allowed to use my Dad’s car last night. (NO difference in meaning when “could not” is used).

general permission.

necessity I must tidy my room (personal obligation: I say so)He has to find a new flat (necessity comes fro outside the speaker)I’ve got to buy a new car.The grass needs cutting OR the grass needs to be cut.He doesn’t have to / doesn’t need to / needn’t type the letter now. (absence of necessity)

She had to find a new flat after she was evicted.

The grass needed cutting OR the grass needed to be cut.

She didn’t have to /didn’t need to buy any bread.)

She needn’t have gone shopping.

(absence of necessity

(It wasn’t necessary for her to go shopping, but she did)

advice You should avoid fatty food.You ought to drive carefully.You had better not drink and drive (it is not a good idea)Shall I ask her out? (asking for advice)Should we buy her a birthday present? (Is it the right, appropriate thing to do).

You should have been more careful.

He ought to have booked tickets.

It would have been better if you hadn’t lied to her.

(but you weren’t)

(but he didn’t)

(but you did.)

criticism He could at least be more polite.They should tell us when there is a change in the timetable.You ought to be more careful of what you say.

He could at least have been more polite.

They could have told us about the conference. You ought to have been more careful.

(but they didn’t)

(It was the right thing to do, but you didn’t do it).obligation I must drink more water ( I need to; I say so)

I have to drink more water (I am obliged to; my doctor says so)We ought to help the poor (it’s the right thing to do, but we don’t always do it)I don’t have to go to work tomorrow (absence of obligation)

I had to drink more water because I was dehydrated.

We ought to have given money to that poor beggar in the street.

(I needed to )

(it was the right thing to do, but we didn’t do it.)

requests Can I use your dictionary?Could I use your dictionary?May I have some water?

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Might I take a seat?Will you lend me 50 pence?Would you mind coming with me?Blue: informalGreen: Formal

offers Can I get you something?Shall I help you with that?Would you like me to do the cleaning?

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suggestions Shall we have a snack?We can always order a takeaway.We could go to the cinema.

If you were so worried about the project, you could have told me.

(but you didn’t)

prohibition You can’t enter the lab. (You’re not allowed to)You mustn’t talk in class (it is forbidden)You may not use the lift (formal)

They couldn’t enter the lab. (they weren’t allowed to)

duty We must attend the meeting.People ought to respect each other. (It’s the right thing to do, but people don’t always do it.)

We had to attend the meeting.

She ought to have told me the truth.

(external obligation)

(It was the right thing to do, but she didn’t do it.)