ADVICE, NECESSITY AND OBLIGATION
GOLDEN RULES ABOUT MODAL VERBS
- Golden rules about modal verbs
- Modal verbs never add an -s in the third person singular:
- He must work harder to pass his exams
- Modal verbs are followed by infinitive without to except from ought to.
- You should behave better!
- Modal verbs don´t need auxiliares to make negative sentences or questions:
- I mustn´t smoke in hospitals
- Modal verbs only have one form. You need other verbs to express the same thing in the past, future etc.
- I´ve been able to finish on time.
We use should and ought to to express advice or make recommendations:
- You should eat less fat if you want to lose weight.
- You ought to relax if you don´t want to get ill.
- You shouldn´t be rude to anybody.
- You oughtn´t to tell lies.
We use need to to express necessity:
Note: Need is not a modal verb.
- We need to buy some bread for lunch.
EXPRESSING OBLIGATION OR NO OBLIGATION
We use must and have to to express obligation. The difference between them is :
- We use must when the obligation is inside the speaker. it is a moral obligation
- We use have to when the obligation is outside the speaker. It comes from the situation.
Note: Have to is not a modal verb.
- I must do some exercise to get fit.
- We have to be quiet in class. That´s the rule.
We use don´t / doesn´t have to, needn´t and don´t /doesn´t need to to express no obligation.
We use mustn´t to express prohibition.
- You don´t need to get up early. It is Sunday!
- she doesn´t need to wear a coat. It is warm outside.
- She needn´t cook tonight. We´re eating out.
- Children under 16 mustn´t go in there
- At school we mustn´t smoke.
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