✏️ Grammar

Modals (Obligation)

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📖 Modals for Obligation

Modal	Use	Example
Must	Strong obligation (speaker's opinion)	"You must respect the law."
Have to	External obligation (rules, facts)	"You have to pay taxes."
Should	Advice, recommendation	"You should vote."
Mustn't	Prohibition	"You mustn't cheat."
Don't have to	No obligation	"You don't have to attend."

✏️ Practice

Choose the correct modal

1. You stop at the red light. (obligation)

2. You eat more vegetables. (advice)

3. You drink and drive. (prohibition)

4. You wear a uniform at school. (external obligation)

MathMaroc · Learning guide

Modals: obligation, advice and deduction

Original practice material · explained answers · no official-exam attribution

Understand the rule

A modal is followed by the base verb without to, except in expressions such as ought to. Can describes ability or permission in context. Should often gives advice. Must can express a strong obligation or a confident deduction; have to often expresses an external requirement. Mustn’t means prohibition, while don’t have to means absence of obligation. May, might and could can express possibility. A perfect modal uses modal + have + past participle to refer to a past situation.

Follow a method

Identify the communicative meaning before selecting a modal. Check whether you are advising, forbidding, describing ability or making a deduction. Distinguish present and past reference. Avoid adding -s to a modal or using two modals together.

Worked example

You mustn’t share another person’s private information: prohibition. You don’t have to print your answer: printing is optional. She must be at school: a confident inference, not a command. She might have missed the bus: a possible explanation about the past.

Practise and explain your answer

01Complete a prohibition: You ___ smoke here.

mustn’t — prohibition, not don’t have to.

02Give advice to a tired student.

You should take a break and organise your revision.

03Correct: He cans speak English.

He can speak English. Modal can has no third-person -s.

04Express uncertainty about a past event.

Example: They might have forgotten the meeting.

05Explain: We don’t have to wear a uniform.

A uniform is not compulsory. Wearing one may still be allowed.