USE

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They are used to talk about, for example,possibility,willingness,abilityobligation,certainty and permission.

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FORM

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-They are always followed by the infinitive without to,except ought .

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- They take the same form in all persons.

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-They don´t use auxiliary verbs to form the interrogative and negative.

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-We sometimes use expressions such as BE ABLE TO , BE ALLOWED TO or HAVE TO, instead of modal verbs for certain meanings and forms which are not possible with modal verbs.

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- When we talk about the past, we can use modal verb+ have+participle. We use this structure, for example, to talk about things that possibly happened or things that did not happen.

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MODAL VERBS