2. General aspects as regards FORM All modal verbs are followed by another verb in its base form. They have no –s /-es in 3 rd Person singular, except for HAVE TO : He has to do an exam and NEED : He needs to buy some petrol. The modal verb is also auxiliary verb: Can I go to the toilets? Should I speak to him? Except for HAVE TO : Does he have to do an exam? and NEED TO : Does he need to buy any food?
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4. ABILITY: can / could / be able to CAN : present events She can speak several languages COULD : past events When she was living in Paris, she could speak French better than now BE ABLE TO : all tenses She is able to speak several languages. She was able to speak French better before. She will be able to speak English better after several classes. She has been able to speak French since she was a child. - Specific ability in a specific past situation . Although she was very nervous, she was able to come out and speak in front of the audience.
5. OBLIGATION: must / have to MUST : the order comes from the speaker itself. Only present or future events . You must be back soon this evening. We’ve got guesses for dinner. - Moral obligation. The duty comes from the speaker. I must study more for the next term. I don’t want to fail this year. HAVE TO : the order comes from an external authority. All tenses and times . I can’t stay longer. I have to come back home. We’ve got some guesses today. - Imposed obligation. We are obliged to do it. I have to study more or my parents won’t let me go to a journey next summer. I have to pay my road taxes today. HAVE TO can be used in the rest of tenses. HAD TO is the past form of MUST . They will have to stay here longer if they don’t finish their work in time. We have had to delay the appointment for the next day. I had to study harder to pass my exams in the last term.
6. Other uses related to Obligation NECESSITY: have to / need to There is no moral obligation implied. I have to buy some more bread for tonight’s dinner. I need to pass all my exams to study at university. PROHIBITION: mustn’t, can’t You mustn’t/can’t speak to each other in an exam. LACK OF OBLIGATION: don’t have to You don’t have to do the exam if you don’t feel well. You can do it another day. I don’t have to get up early tomorrow. It’s a holiday.
