21st November
Expressing possibility, obligation, permission and prohibition
 Possibility: may & might
E.g. They may know about the party.
They might know about the party.
– May expresses a greater degree of possibility than might.
 Obligation and necessity: must, have to & be supposed to
E.g. I must read the book. (The obligation is imposed by the speaker.)
The have to present the projects in front of the class. (The obligation is imposed by
someone else.)
We are supposed to do our homework at home. (This is the rule, but we don’t always
follow it.)
 No obligation or necessity: don’t have to & don’t need to
E.g. You don’t have to go to the party if you don’t want to.
We don’t need to buy any carrots for the soup. My mum bought some yesterday.
 Permission: let & be allowed to
E.g. They let us use their equipment.
We are allowed to use their equipment.
 Prohibition: not be allowed to, doesn’t/don’t let, mustn’t
E.g. The students are not allowed to enter the lab before the teacher.
They don’t let the students enter the lab before the teacher does.
The students mustn’t enter the lab before the teacher does.
 Something is / isn’t a good idea: should / shouldn’t
E.g. I should learn more. I have bad grades.
I shouldn’t stay up so late every evening. I’m always tired.