Modals verbs

Express obligation

We use have to/has to to talk about rules or laws which were made by someone else or which we may not agree with

Example: I have to show my passport when I cross the border

We use had to when we talk in past.

Express obligation

We use must to talk about rules or laws which we agree with or believe in.

Example: You must take your passport with you everywhere you go

We use don´t have to/doesn´t have to when it is not necessary to do something.

Example: My brother doesn´t have to wear an uniform in the new school.

We use didn´t have to when we talk in past.

We use mustn´t to express prohibition

In the past tense we use not allowed to instead of mustn´t

Example: On a plane, we mustn´t use the phone

We use can/can´t to express permission or lack of permission.

Example: Can I use your phone, please?

We use could/ couldn´t when we talk in past.

We use should/shouldn´t to give or ask for advice

Should/shouldn´t is followed by the infinitive without to.

An alternative of should is ought to. Only for positive sentences.

Example: If you want to keep fit, you should go to the gym.