Modals of obligation, necessity and prohibition

Modals of obligation, necessity and prohibition

MODAL VERBS

No obligation/necessity

Prohibtion

Obligation/ necessity

You have to wear a seatbelt in a car. I must remember to call Emily tonight - it's her birthday. We need to follow trends.

You mustn't leave the designated area. You aren't allowed to bring mobile phones into the lab.

You don't have to pay for the tickets. They're free. You don't need to wear an ID badge. It isn't mandatory.

We are supposed to park at the back of the building.

• Must has no past or future form. For the past and the future use have to
• Must is rarely used in questions - we use have to
• It is possible to use needn't instead of don't need to
• Have to is more commonly used by native speakers than must, because the latter may sometimes seem rude or aggresive.

Must and have to

Have to is more common for general, external obligations, for example rules and laws. I have to wear a shirt and tie at work. (It's the rule in this company)

Must is more common for specific (on one occasion) or personal obligations. I must buy a new shirt - this one is too old now. (it's my own decision).

You can also use have to or must for strong recommendations: You have to/ must see that film - it's fantastic!

Remember

• with must and should don't use auxiliary verbs (do, did, have, etc.)
• have to takes the auxiliary as a regular verb

Compare:

• Should I help them?
• You mustn't use this computer.

• You don't have to go to that party.
• Did you have to wear uniforms at school?