modals情态动词.docx

Modals (1)Permission, Prohibition, Obligation, No obligationTo expresspermission,prohibition,obligationand noobligationwe usually use modal verbs.PermissionCanis often used to ask for and give permission. Can I sit here? You can use my car if you like. Can I make a suggestion?We can also usemayandcouldto ask for and give permission butcanis used moreoften.ProhibitionBothcantandmustntare used to show that something is prohibited it is not allowed. You cant park here, sir. You can wear jeans but you cant wear trainers in that bar. You mustnt speak when the teacher is speaking.Canttells us that something is against the rules.Mustntis usually used when the obligation comes from the person who is speaking.ObligationHave toandmustare both used to express obligation. There is a slight difference between the way they are used.Have toshows us that the obligation comes from somebody else. Its a law or a rule and the speaker cant change it. Do you have to wear a uniform at your school? John cant come because he has to work tomorrow. In Britain you have to buy a TV licence every year.Mustshows us that the obligation comes from the speaker. It isnt a law or a rule. I must call my dad tonight. You must hand in your homework on Tuesday or your mark will be zero. You must come and visit us the next time you come to London.No obligationWe usedont have toto show that there is no obligation. You can do something if you want to but its not compulsory. You dont have to wear a tie in our office. You can wear a tie if you want to but its OK if you dont. Itll be nice if you do but you dont have to come with me if you dont want to. You dont have to dress up for the party. Wear whatever you feel comfortable in.Modals deduction (present)We use modal verbs to say how sure we are about something.1 mustWe usemustwhen we feel sure that something is true because theres very strong evidence. He must live near here because he comes to work on foot.We dont know where he lives but were sure its not far away. Come inside and get warm you must be freezing out there. Youre a zookeeper? That must be very interesting.Notice thatmustis followed by an infinitive without to.2 might, may, couldWe usemight,mayorcouldto say that we think something is possible but were not sure. Did you hear that? I think there might be a burglar downstairs.Shes not sure theres a burglar but she thinks its possible. Well try to get there early but we may arrive late if theres a lot of traffic. Dont put it up there. It could fall off and hit someone.Might,mayandcouldare also followed by an infinitive without to.3 cantWe usecantwhen we feel sure something is not true. It cant be a burglar. All the doors and windows are locked.He doesnt know its not a burglar but he feels sure its not. It cant be far away now. Weve been driving for hours. Wheres the map? Really? He has to work on Christmas Day? He cant feel very happy about that.Like the other verbs,cantis followed by an infinitive without to.Remember that all of these modal verbs must,might,may,couldandcanthave other uses. These are covered in another section.Modals deduction (past)In the same way that we use modal verbs to say how certain we are about things in the present we can also use them to speculate about the past.Have + past participle(have done, have been have stolenetc.) is called theperfect infinitive. When we use modal verbs to talk about the present they are followed by an infinitive without to. When we use modal verbs to talk about the past they are followed by a perfect infinitive.must + perfect infinitiveWe usemust + perfect infinitivewhen we feel sure about something in the past. You must have been delighted when you heard youd won the lottery. The thieves must have come in through the window. Look its still open. Oh no! Wheres my car? Someone must have stolen it!might/may/could + perfect infinitiveWe usemight,mayorcouldwith theperfect infinitiveto say that we think something was possible but we arent sure. The thieves might have escaped by car but we cant be sure. He should be hour by now. He may have been delayed by a traffic jam or something. I cant find my purse. I could have left it in the supermarket but I just dont know.cant + perfect infinitiveWe usecant + perfect infinitivewhen we feel sure something didnt happen in the past. I thought I