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Expressing Necessity in English
In English, we can use different modals, semi-modals, and verb phrases to express necessity and obligations and each has its specific nuances.
Using 'Must'
The modal verb 'must' can be used to express a strong necessity and obligation.
As a modal verb, 'must' is followed by the base form of the verb and has the same form for all subjects. 'Must' can refer to both present and future.
You must be there on time.
I must study today. Let's go out tomorrow.
Making Questions
'Must' is not commonly used to form questions, but when it is, it moves before the subject. For example
Must I finish it by 10 pm?
Must they fasten their seat belts?
Using 'Have to'
Another way to express necessity and obligation is to use 'have to.' Using 'have to' is more common in English as it can adapt to different tenses as well as negative and interrogative forms.
You have to clean the house.
In some religions girls have to wear scarves.
Making Questions
Using 'have to' in interrogative sentences is very common. Unlike modals, 'have to' needs the supporting auxiliary verb (do/does/did) to form questions and negative sentences.
Do we have to wait for him?
Did he have to write five articles in one day back then?
'Must' vs. 'Have to'
'Must' and 'have to' are sometimes used interchangeably in everyday usage. However, the source of obligation is typically different. While 'must' is often used when convey the speaker's personal authority or strong advice, 'have to' usually refers to an external rule or requirement. For example:
I must clean up my room. It is really messy.
You must confirm your name before entering Miss.
I have to pay my taxes.
Maria has to submit her homework by the mentioned deadline.
Using 'Have Got to'
Another way of expressing obligation and necessity is to use the verb phrase 'have got to'. This structure is more common in informal contexts or conversations.
You've got to start taking responsibility for your actions.
I have got to go. There is a party at 7.
Making Questions
As the verb 'have' in the phrase 'have got to' is an auxiliary, to make a question, all we have to do is invert the subject and the auxiliary verb 'have.'
Has she got to pick up John from school?
Have you got to set up the blind date for them?
Using 'Shall'
'Shall' is a modal verb that can be used in legal, contractual, or formal writing to show that something is required or obligatory. For example:
You shall pay the rent at the beginning of the month.
Employees shall wear identification badges at all times.
Making Questions
Since 'shall' is a modal verb, it simply moves to the beginning of the sentence to form a question. In other words, it undergoes inversion and switches its place with the subject of the sentence. Here are some examples:
Shall I submit the report by Friday?
Shall we include this point in the minutes?
Using 'Should'
'Should' is the past tense of the modal verb 'shall'. However, it does not actually refer to the past. 'Should' refers to obligations in the present or future, but it is different from 'shall' in that the obligation is more of a moral kind or a personal advice.
I should pay more attention.
We should take her to the hospital.
Using 'Need'
The verb need can be used as either a modal verb or a main verb. In both cases, it can express necessity and obligation. Keep in mind that the modal 'need' is mainly used in negative sentences and questions and always followed by the base form of the verb. The main verb, however, is used in affirmative as well as non-affirmative contexts and followed by to-infinitives.
You need to send all the emails within two days.
You need not worry about it.
Making Questions
If we use 'need' as a main verb, we have to add the supporting auxiliary (do/does/did) at the beginning of the sentence to make an interrogative sentence.
If we use 'need' as a modal verb, we need to put it at the beginning of the sentence, before the subject, to form a question.
Do we need to leave the building?
Need I remind you of your past?
Using 'To Be Supposed to'
'To be supposed to do something' is an expression that is used to say that the subject is required to do something. You can change the tense of the verb be, to adapt this expression to different tenses. You can also change its place with the subject to form questions about obligations. Check out the examples:
She is supposed to be here at 10.
I was supposed to fill up the car.
Necessity and Obligation: Past Tense
Had to
'Must' and 'have got to' do not have a past form. 'Have to' is the only member of this set which has a past tense ('had to'). So when talking about an obligation or necessity in the past, the options are more limited that the present tense. Here are some examples:
We had to be on time for the meeting.
The plane had to take off immediately.
Needed to
The modal verb 'need' does not have a past form, but the main verb alternative can be changed into past tense to talk about a past necessity. For example:
I needed to stop there to buy some stuff.
Anna and Pam needed to answer two questions, each.
Should Have
You can use 'should have' before 'past participles' to refer to things that were supposed to be done in the past, but were not. This usage conveys a sense of regret.
I should have seen him before it was too late.
Marry should have waited for me to pick her up.
Negation
Apart from the modal 'need' and 'have (got) to' which show a lack of necessity in the negative form, the other modals can take 'not' after them to show a negative obligation. In other words, when 'not' is added after 'must,' 'shall,' and 'should,' the sentence shows that action is prohibited.
You needn't worry for him anymore, he turned thirty last year.
This shows a lack of necessity.
I haven't got to go now.
You must not work out when your muscles are hurt.
This sentence shows that working out is prohibited in case of an injury.
You shall not enter the building without an ID.
Using Auxiliary 'Do'
When 'have to' and 'need' are used as a main verb, they need the supporting auxiliary do/does/did to be negated. Here are some examples:
You did not have to do my dishes.
She didn't need to work. Her father was a merchant.
Review
There are some modals and verb phrases that are used to talk about necessity and obligation, including:
must
have to
have got to
need (to)
shall
should
be supposed to
Quiz:
Sort the words to form a question about obligations.
Which sentence correctly shows a past obligation?
We have to finish the project yesterday.
She has to leave early tomorrow.
They had to attend the meeting last week.
I must have submitted the report on time.
Which sentence shows a prohibition (negative obligation)?
You needn't bring food; there's plenty here.
You must not park here—it's a fire lane.
She doesn't have to work weekends.
They should not be late.
Match the sentences to their meanings.
Fill the blanks with the appropriate modal/verb phrase. (There are two extra options.)
I tell him the truth?
I
saved more money last year.
We
be more careful with confidential documents.
I
wake up early yesterday for my flight.
You
bring all this stuff for the trip. Take only essentials.
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