American English

Definition of have to modal verb from the Oxford Advanced American Dictionary

      

    have to

     modal verb
    modal verb
    NAmE//ˈhæf tə//
     
    , NAmE//ˈhæftu//
     
     
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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've got to leave by 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?
  2. 2(also have got to) 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) used to say that something must be true or must happen There has to be a reason for his strange behavior. This war has got to end soon.
  4. 4used to suggest that an annoying event happens in order to annoy you, or that someone 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) Grammarmodal verbsThe 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 past or present participles 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 and used to:You must find a job. You ought to stop smoking. I used to smoke, but I quit 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 shouldn't invite Mary. The error will not have affected our results.You will find more help with how to use modal verbs at the dictionary entries for each verb. Grammarmust / have (got) to / must not / don’t have tonecessity and obligationMust and have (got) to are used in the present to say that something is necessary or should be done.Have to is more common, especially in speech:You have to be home by 11 o’clock. I have to wash the car tomorrow. I have to collect the children from school at 3 o’clock.Must is stronger and more formal:All nurses must wear uniform. Changes must be recorded in the log book.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 uniforms?In negative sentences, both must not and don’t have to are used, but with different meanings. Must not is used to tell someone not to do something:Employees must not smoke in the building.The short form mustn’t is rare and very formal: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 on weekends.certaintyBoth must and have (got) to are used to say that you are certain about something. Have to is the usual verb in this meaning:He has (got) to be the worst actor on TV!If you are talking about the past, use must have:Your trip must have been fun!
See the Oxford Advanced Learner's Dictionary entry: have to