SUMMARY OF FUNCTIONS OF MODAL VERBS USE ability/ lack of ability
possibility
probability
deduction and speculation
permission
PRESENT/ FUTURE She can drive a car She’s able to use a PC. He can’t play the piano
PAST 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 He can still be at home (90% certain) We could have been injured, but luckily we She could still be at home (50% certain) weren’t. Steve may be working late (50% certain ) Mary may have fallen asleep (perhaps she has) She might be a little late (40% certain; perhaps Lucy might have tried to contact us (perhaps she she will be late) has) It is likely that they will come with us (90% cettain) It was likely that she had missed the last bus. David is unlikely to fly to Rome (90% certain that She was unlikely to have missed the last bus. he won’t fly) He is bound to get that job he wants. (95% certain) He will be home soon. (100% certain; this is a She should have called by now. (She probably prediction based on knowledge of the person’s has called) habits) he should pass the test (9’% certain; future only, He ought to have gone to bed by now (he it’s very probable. probably has already gone to bed.) They ought be home by now (90% certain they will probably be home in a minute – otherwise, the speaker will be seriously worried. She must be tired (90% certain – positive; I’m She must have completed the race. sure she’s tired) They can’t be rich! (negative; I’m sure they aren’t rich) She can’t have lost her keys again! He couldn’t be at work (negative; I’m certain he isn’t at work) They couldn’t have called in to see us! 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)
NOTES 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,
(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), (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)
necessity
advice
criticism
obligation
requests
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 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) 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). 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. 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) Can I use your dictionary? Could I use your dictionary? May I have some water?
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.
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.) (absence of necessity She needn’t have gone shopping. You should have been more careful.
(It wasn’t necessary for her to go shopping, but she did) (but you weren’t)
He ought to have booked tickets.
(but he didn’t)
It would have been better if you hadn’t lied to her.
(but you did.)
He could at least have been more polite.
(but they didn’t)
They could have told us about the conference. You ought to have been more careful. I had to drink more water because I was dehydrated.
(It was the right thing to do, but you didn’t do it). (I needed to )
We ought to have given money to that poor beggar in the street.
----------------
(it was the right thing to do, but we didn’t do it.)
offers suggestions prohibition duty
Might I take a seat? Will you lend me 50 pence? Would you mind coming with me? Blue: informal Green: Formal Can I get you something? Shall I help you with that? Would you like me to do the cleaning? Shall we have a snack? We can always order a takeaway. We could go to the cinema. 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) 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.)
---------------If you were so worried about the project, you could have told me.
(but you didn’t)
They couldn’t enter the lab.
(they weren’t allowed to)
We had to attend the meeting.
(external obligation)
She ought to have told me the truth.
(It was the right thing to do, but she didn’t do it.)