Tham khảo tài liệu 'grammar practice for upper intermediate students_5', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Modal auxiliaries We can also use have got to to express obligation. Have got to is often interchangeable with have to but there is sometimes a difference. Have to can be used for habitual actions and single actions I have to get the bus into work today. I have to get the bus into work every day. Have got to can only be used for single actions I have got to get the bus into work today. NOT I have got to get the bus into work every day. To express a negative obligation use mustn t. Do not use don t have to. Don t have to means there is no obligation You mustn t wait here. You are not allowed to wait here. You don t have to wait here. It is not necessary for you to wait here but you can if you want to. To express obligation in the past use had to I had to report the incident to the police. Did you have to get a visa Note Must perfect infinitive is not used to talk about past obligation. It is used to make deductions about the past She must have left early. To express necessity use need. We can use need as a modal verb in questions and negative sentences. It is most often used in the negative You needn t come if you don t want to. Need I bring anything with me We can also use need as an ordinary verb followed by the to-infinitive You don t need to come if you don t want to. Do I need to bring anything with me Everyone needs to eat fresh fruit and vegetables. I ll need to buy some new clothes if I get that job. To express lack of necessity in the past use needn t perfect infinitive or didn t need to didn t have to infinitive. There is some difference between them I needn t have gone to the station so early. The train was nearly an hour late. It wasn t necessary to go to the station early but I didn t realise that and so I did get there early. We didn t need to didn t have to get up early this morning because we had no lectures. It wasn t necessary and so we didn t do it. Note We do not use need perfect infinitive in the positive. 104 Modal auxiliaries Practice 36 .
