Definition of have to modal verb from the Oxford Advanced Learner's Dictionary

      

    have to

     modal verb
    modal verb
    BrE BrE//ˈhæv tə//
     
    ; NAmE NAmE//ˈhæv tə//
     
    ; BrE BrE//ˈhæf//
     
    ; NAmE NAmE//ˈhæf//
     
    Verb Forms present simple I / you / we / they have to
    BrE BrE//ˈhæv tə//
     
    ; NAmE NAmE//ˈhæv tə//
     
    ; BrE BrE//ˈhæf//
     
    ; NAmE NAmE//ˈhæf//
     
    he / she / it has to
    BrE BrE//ˈhæz tə//
     
    ; NAmE NAmE//ˈhæz tə//
     
    ; BrE BrE//ˈhæs//
     
    ; NAmE NAmE//ˈhæs//
     
    past simple had to
    BrE BrE//ˈhæd tə//
     
    ; NAmE NAmE//ˈhæd tə//
     
    ; BrE BrE//ˈhæt//
     
    ; NAmE NAmE//ˈhæt//
     
    -ing form having to
    BrE BrE//ˈhævɪŋ tə//
     
    ; NAmE NAmE//ˈhævɪŋ tə//
     
     
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  1. 1  (also have got to) used to show that you must do something Sorry, I've got to go. Did she have to pay a fine? You don't have to knock—just walk in. I haven't got to leave till seven. First, you have to think logically about your fears. I have to admit, the idea of marriage scares me. Do you have to go? (especially British English) Have you got to go? Express YourselfAsking about obligationWhen you are unsure about what is expected of you in a situation, you can ask about obligations: What time do we have to be home? Are we supposed to show our ID cards? Is it necessary to apply for a visa? Is there a legal obligation to wear a bike helmet here?
  2. 2  (also have got to especially in British English) used to give advice or recommend something You simply have to get a new job. You've got to try this recipe—it's delicious.
  3. 3  (also have got to especially in British English) used to say that something must be true or must happen There has to be a reason for his strange behaviour. This war has got to end soon.
  4. 4used to suggest that an annoying event happens in order to annoy you, or that somebody does something in order to annoy you Of course, it had to start raining as soon as we got to the beach. Do you have to hum so loudly? (= it is annoying) Grammar Pointmodal verbs The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs. Modal verbs have only one form. They have no -ing or -ed forms and do not add -s to the 3rd person singular form:He can speak three languages. She will try and visit tomorrow. Modal verbs are followed by the infinitive of another verb without to. The exceptions are ought to, have to and used to:You must find a job. You ought to stop smoking. I used to smoke but I gave up two years ago. Questions are formed without do/does in the present, or did in the past:Can I invite Mary? Should I have invited Mary? Negative sentences are formed with not or the short form -n’t and do not use do/does or did.You will find more help with how to use modal verbs at the dictionary entries for each verb. Grammar Pointmust / have (got) to / must not / don’t have toNecessity and Obligation Must and have (got) to are used in the present to say that something is necessary or should be done. Have to is more common in North American English, especially in speech:You must be home by 11 o’clock. I must wash the car tomorrow. I have to collect the children from school at 3 o’clock. Nurses have to wear a uniform. In British English there is a difference between them. Must is used to talk about what the speaker or listener wants, and have (got) to about rules, laws and other people’s wishes:I must finish this essay today. I’m going out tomorrow. I have to finish this essay today. We have to hand them in tomorrow. There are no past or future forms of must. To talk about the past you use had to and has had to:I had to wait half an hour for a bus. Will have to is used to talk about the future, or have to if an arrangement has already been made:We’ll have to borrow the money we need. I have to go to the dentist tomorrow. Questions with have to are formed using do:Do the children have to wear a uniform? In negative sentences both must not and don’t have to are used, but with different meanings. Must not is used to tell somebody not to do something:Passengers must not smoke until the signs have been switched off. The short form mustn’t is used especially in British English:You mustn’t leave the gate open. Don’t have to is used when it is not necessary to do something:You don’t have to pay for the tickets in advance. She doesn’t have to work at weekends.Certainty Both must and have to are used to say that you are certain about something. Have to is the usual verb used in North American English and this is becoming more frequent in British English in this meaning:He has (got) to be the worst actor on TV! (British English) This must be the most boring party I’ve ever been to. If you are talking about the past, use must have:Your trip must have been fun!
See the Oxford Advanced American Dictionary entry: have to