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Modal Verbs of Obligation & Advice

Learn how to talk about obligations and to give advice with modal verbs.

Modal verbs are special verbs that give other verbs more meaning. They can describe how, when, or why another action happens. Two ways that you can use modal verbs

are to describe obligations and give advice.

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Describing Obligations

You can talk about obligations or things that are absolutely necessary using must. For things that are forbidden, as in it is necessary that you don’t do it, you can use mustn’t and can’t / can not.

For Example,

  • You mustn’t smoke in the restaurant. / You can not smoke in the restaurant.

  • You must be here 10 minutes before the exam.

  • We must prepare a report by the end of the month.

Other ways to express obligation

We can also use ‘have to’ / ‘don’t have to’ and should/ shouldn’t to talk about obligations.

‘have to / don’t have to’

  • My sister has to start school in September. (it is necessary for her to start in school September)

  • You don’t have to go to University. (it is not necessary to go to University)

should/ shouldn’t

You can also use should/ shouldn’t to express an obligation in a more gentle way.

  • You really shouldn’t smoke inside, there are children here. (= politely telling someone that it is necessary for them to NOT smoke inside).

  • The dog should be outside. (it is necessary for the dog to be outside and I’m telling you politely)

Making Suggestions

When you want to give advice or make strong suggestions, use should, shouldn’t, could or shall.

Should, Shouldn't

Use should or shouldn't when you want to give very strong advice or suggestions.

For Example,

  • You should try Korean food, it’s delicious!

  • He shouldn’t give her so much candy, it isn’t healthy.

  • You should speak English every day if you want to improve.

  • Shall we have dinner at 9?


You can use could to make positive suggestions. Be aware, the difference between could and should is that should is much stronger. Use could if you just want to give advice on what options are available for something.

For example,

  • We could eat pizza tonight.

  • You could try rebooting your computer.

  • She could go with her friends after school, or she could come with us.

  • We could cook ramen noodles tonight for dinner.

Review how to form modal verbs in a sentence here.

Practice using modal verbs of obligation and advice

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