You must wear a seatbelt. They must

In English there are various ways to describe rules and obligations, and as a student it can be tricky to understand which way is right for each situation. Here is a description of each modal verb that we use to express obligation and how and when to use them.

Must

‘Must’ is the basic and most direct way of saying something is compulsory. It means you have no choice but to do (or not do) an action. We can only use ‘must’ in the present form to describe a general or permanent obligation, or an obligation in the near future. The structure of ‘must’ is easy because it is the same for every subject:



Here are some examples:



When you drive you must wear a seatbelt.

They must hand in their projects before the 8th June.

I must remember to send a birthday card to my Dad.

He must study harder if he wants to pass the exam.

We must get to the airport two hours before the flight.

To make negative sentences we add ‘not which is normally contracted to n’t:



We use ‘mustn’t’ to express a prohibition or strong obligation. For example:

When the traffic lights are red you mustn’t go.

They mustn’t use their mobile phones during lessons.

We mustn’t stand up while the plane is taking off.

I mustn’t drink any more coffee, otherwise I won’t sleep tonight.

She mustn’t go outside without a jacket. It’s really cold.