Today I’m going to give a a quick guide to the modal verbs ‘ought’, ‘must’ and ‘need’. For other modals, see last week’s post.
‘Have to’ is used to indicate an obligation. It is weaker than ‘must’.
“I have to go to the dentist at one o’ clock today.”
“Don’t you have to finish your homework?”
‘Don’t have to’ or ‘haven’t got to’ is used to say that an action is unnecessary. One may do the action but if one does not, it is acceptable.
“You’re a guest. You don’t have to wash the dishes.”
“I haven’t got to do anything tonight so do you want to watch the telly?”
In its positive form, ‘have to’ can be used to speculate.
“It has to be minus ten degrees outside today. I’m freezing.”
“You have to be serious about passing that test. You haven’t stopped studying for four hours.”
Must is used to indicate a strong obligation. It is not a recommendation. It is extremely strong and can appear impolite or bossy if used in the wrong situation. It is much stronger than ‘have to’.
“I must get up early tomorrow. I have so much work to do.”
“You must come out with us tonight. It will be so much fun.” (This is not rude; it is a strong invitation.)
In its negative form, ‘must not’ or ‘mustn’t’, it is used to say that something is forbidden. ‘Must not’ has a very different meaning to ‘don’t have to’ or ‘haven’t got to’.
“You must not put knives and forks in the microwave.”
“You mustn’t be late because the teacher is very strict about that.”
However, both positive and negative forms of ‘must’ are used for speculation, that is guessing about situations.
“A lot of people are carrying umbrellas. It must be raining.”
“She hasn’t eaten a thing. She mustn’t be hungry or she must hate my cooking.”
‘Need to’ is used for strong obligation. It is slightly weaker than ‘must’ but stronger than ‘have to’.
“I am going to go home now. I need to do my homework.”
“Do you need to do it tonight?”
In its negative forms, ‘do not need to’, ‘need not’ or ‘needn’t’, it indicates that an action is unnecessary like ‘don’t have to.’
“I needn’t study tonight. The test isn’t until next week.”
“I don’t need to wash the car today. It’s going to rain later.”
‘Ought to’ is used to strongly recommend actions. It often sounds formal. It is stronger than ‘should‘.
“You ought to study English every day. You’ll get better quickly.”
‘Ought not (to)’ or ‘oughtn’t’ is used to strongly recommend against doing actions. It also sounds formal. Again, it is stronger than ‘shouldn’t‘
“You oughtn’t study while listening to music.”
“There is no fine for returning books to the library late but you ought not to do it because other students may be waiting for the books.”