POSSIBILITY, OBLIGATION, NECESSITY,PERMISSION, PROHIBITION

POSSIBILITY, OBLIGATION, NECESSITY, PERMISSION, PROHIBITION, ADVICE

POSSIBILITY

We can talk about possibility by using some modal verbs or some structures with modal value.
1. MAY (for specific situations)
eg. I may visit you tomorrow. (=Maybe I will visit you tomorrow.)
2. MIGHT (for specific situations)

eg. They might be at home. (=Maybe they are at home.)
3. COULD (for specific situations)

eg. She could call you back tonight. (=Maybe she will call you back.)(informal use)

POSSIBILITY

4. CAN (to make general statements about what is possible)

eg. It can be very cold here in winter. (= It is sometimes very cold here in winter.)
eg. You can easily get lost in this town. (= People often get lost in this town.)

We do not use can to express posibility about specific events!

A: Where's John?
B: I'm not sure. He may/might/could be (NOT can) in his office.

We can talk about obligation and necessity by using:
1. MUST (obligation)
eg. You must get there before eight o’clock. (= This is an obligation imposed by the speaker.)
2. HAVE TO (obligation)
eg. We have to finish our projects by Friday. (= This is an obligation imposed by someone else.)
3. BE SUPPOSED TO (obligation)

eg. We’re supposed to switch off our phones in lessons. (= This is the rule, but we don’t always follow it.)

​​​OBLIGATION AND NECESSITY

4. NEED TO (necessity)

eg. You need to clean your room. It'a a mess!

We can talk about no obligation or no necessity by using:

1. DON'T HAVE TO (no obligation)
eg. You don’t have to eat this if you don’t want to.

2. DON'T NEED TO (not necessary)
eg. We don't need to buy tickets - my dad will give us some.

OBLIGATION AND NECESSITY

We use dindn't need to and needn’t have to to talk about the past necessity of actions. There is a small but important difference between the structures.

1. DIDN'T NEED TO usually suggests that we didn’t do something because it wasn’t necessary.
eg. I didn’t need to go to the doctor. (I didn’t go.)
2. NEEDN'T HAVE TO means that we did something but actually it wasn’t necessary.
eg. We needn’t have cooked all this food - only four people turned up at the party. (We cooked a lot of food but it wasn’t necessary.)

NECESSITY:"didn’t need to / needn’t have"

We can talk about permission using LET or BE ALLOWED TO.
Let is active voice, while be allowed to is passive voice.

eg. The school lets us use the tennis courts at the weekend.
eg. We’re allowed to use the tennis courts at the weekend.

We can talk about prohibition using NOT BE ALLOWED TO or DON'T/DOESN'T LET. When we don’t know or don’t want to say who it is that prohibits something, we use ‘they’.
eg. Cyclists are not allowed to leave their bikes here.
eg. They don’t let cyclists leave their bikes here.

PERMISSION and PROHIBITION: "let"and "be allowed to"

We can give advice or say something is a good idea by using:
1. SHOULD (advice)
eg. You should leave now if you don’t want to miss your bus. I shouldn’t eat any more or I’ll feel sick.
2. HAD BETTER ( 'D BETTER) (strong advice)(bad consequences)
eg. We'd better go or we'll miss the train!

We can say something is not a good idea or give a warning by using:
1. SHOULDN'T
eg. They shouldn't buy that house. It's too expensive.
2. HAD BETTER NOT
eg. You'd better not do that or else!

ADVICE: "should" and "had better"