obligation, permission, advice, prohibition

On the left hand side you have the grammar explanation. On the right hand side you have an exercise to test your knowledge of the grammar. Complete the second sentence so that it has the same meaning as the first sentence. Write between 2 and 5 words. You must use the key word without changing it. Each question has a clue, so if you need some extra help, click on the yellow word Clue? below the question. If you want to hide the clue, click on it and it will disappear. Think hard now...

Can: can I go to the toilet please?
May: may I suggest something?
To let: my parents let me stay up late every weekend.
To allow: Are we allowed to go into this room?

Can: she said I could go to the concert, so I went
to allow: her boyfriend never allowed her to speak with other men. I think that's why she left him.
to let: his boss didn't let him have time off because there was too much work to do.

Can: you can use my car tomorrow if you like.
To allow: will you be allowed to speak to her?
To let: I don't think your mum will let you borrow her car.

You cannot use "may" in the past for permission
You cannot use "let" in the passive

could: you could have sent her some flowers
should: you should have worn a suit for the interview
ought to: he ought to have told you the truth

When you use "could", "ought to" and "should" in the past for advice, notice that they need to be followed by the perfect infinitive: (have + past participle)

Present and Future
could: you could always change your mind
should: I think you should take the job. It sounds great.
had better: you had better go now
ought to: you ought to apologise to them
must: you must go and see that film
to have to: you have to meet her, she is lovely

Notice that "had better", "must", and "have to" are not used in the past to give advice.

Other points of interest

"Should" gives stronger advice than "could". Though "have to" and "must" give the strongest advice.

All of these expressions are followed by the infinitive. Notice that if you want to make the infinitive negative, you need to put "not" before it:
You had better not phone him.
You ought not to go there.

Couldn't: My boss said that I couldn't leave early
Not allow (active): Daves mum didn't allow him to smoke at home.
Not allow (passive): Simon was not allowed to drive his car because he had lost his licence.
Not let: she didn't let him finish what he was saying.

Present and Future
can't: you can't come in, this is for ladies only.
to not allow: dogs are not allowed on this beach.
may not: -can I watch TV mum?
-no, you may not.

to not let:I won't let him hurt you again.
mustn't: you mustn't tell her. It's a secret.

Notice that "may not" and "must not" cannot be used in the past.

Notice that "not let" is followed by the infinitive without "to". Also, "not let" cannot be used in the passive.

to have to: I had to get up very early in my previous job.
to make: my teacher made me do extra work if I behaved badly.

Present and Future
must: you must give me the money tomorrow, or I won't be able to buy the tickets for the plane.
to have to: drivers have to drive on the left in England.
to make (active): my parents make me do the washing up every day
to make (passive): I was made to stand up in front of the class and recite a poem.

Notice that we cannot use "must" in the past to talk about obligation.

Remember that "make" is followed by the infinitive without "to" in the active, but with "to" in the passive.

No obligation
don't have to: You don't have to come if you don't want to.
don't need to: She doesn't need to pay full price because she is a student.
needn't: You needn't bring anything for the dinner. Just your company will be fine.

Finally, compare the following using "need" to talk about the past:
-You needn't have bought me a present. (it wasn't necessary but you did)
-You didn't need to buy me a present. (it wasn't necessary, and it is not known if you did or not)