Modal verb

Modals: May, Might, Can, Could, Shall, Should, Will, Would, Must

Semi Modals: Have to, Used to, ought to, need

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1- Possibility: May (not) + Might (not) + can + could

May is usually slightly more sure than Might and Could

couldn't dosen't mean the same as may/might not.

can is used for more general, theoretical possibility

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2- Ability: Can + could

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3- Inability: Can't + Couldn't

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4- Prohibition: Mustn't

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5-Strong Obligation: Must +Have to + had to

Must refers to strong present and future obligations, imposed or accepted by speaker

have to refers to strong present and future obligations

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6- Weak Obligation: Should + ought to

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7- necessity: Need

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8- Lack of necessity: Needn't or dont need

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9-Lack of obligation: Don't have to