Have to, Don't have to, Mustn't, Should/Shouldn't

​We use have to to indicate that something is necessary.

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​You have to train hard to become a great champion.

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​Don't have to indicates that it's not necessary. (It's up to the person.)

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​You don't have to go to the gym to train hard. (It's not necessary as you can train hard anywhere.)

​Form

​Have to/Don't have to + Base verb

​I, You, We, They have/don't have to

​He, She, It has/doesn't have to

​- To prohibit or stop somebody from doing something, we use mustn't. (rule)

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​You mustn't go near that lake: it's infested with crocodiles.

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​- Mustn't is always followed by a base verb.

​You mustn't go.

​Should and shouldn't are used to give advice.

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​- Should is used to tell someone it's good idea to do something.

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Maybe you should start a new paragraph here.​

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​- Shouldn't is to say that it's good they don't do it.

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​You shouldn't have more than one idea in your paragraph.

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​Should/Shouldn't + Base Verb

​Question form

​Should/Shouldn't+ Subject + Base Verb

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Shouldn't you begin a new paragraph here?