Grammar
Modal verbs for obligation: must, have to, and need to
You must turn off your phone. You have to turn off your phone. You need to turn off your phone. Each sentence points to an obligation, but the reason and tone can change.
Choose must, have to, or need to by identifying the source of an obligation, then form negatives, questions, and past obligations accurately.
Read and practice
Read the examples and try the written questions in this guide. Listening recordings are not available for this lesson yet.
Try the written questions
You have to show your pass at the gate. /juː hæv tə ʃəʊ jɔː pɑːs æt ðə ɡeɪt/
The short answer
Must gives a strong instruction or personal sense of duty. Have to often reports an outside requirement. Need to says that an action is necessary. After must, use a base verb. Have to and need to use to before the verb.
The lab assistant must lock the cabinet.
Why it works: Must makes locking the cabinet a firm instruction. Lock is the base verb after must.
5 more examples
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I must call the landlord before noon.
The speaker presents the call as a firm personal duty.
Not this:I
have to callthe landlord before noon because the office closes. What changes: The office schedule explains why the call is required. -
Every guest has to sign the visitor log.
The visitor procedure creates the requirement for every guest.
Not this:Every guest
must signthe visitor log. What changes: Must gives the rule in a more direct voice. -
You need to save the receipt for the return.
Saving the receipt is necessary if the person wants to return the item.
Not this:You
should savethe receipt for the return. What changes: Should gives advice, while need to states a necessary step. -
You must not leave tools on the stairs.
Must not says that leaving tools there is prohibited.
Not this:You
do not have to bringyour own tools. What changes: Do not have to means that bringing tools is optional. -
Ravi had to reschedule the appointment last week.
Had to reports a requirement that existed in the past.
Not this:Ravi
will have to reschedulethe appointment tomorrow. What changes: Will have to moves the requirement into the future.
Read the full guide
Look at the reason before you choose the form. A speaker can use must to give an instruction directly. A posted rule, a deadline, or a practical problem often leads to have to. Need to is useful when the sentence simply says that an action is necessary.
Find the source of the obligation
Before choosing a form, ask why the action is required. Is the speaker giving a direct instruction? Does a rule or timetable require the action? Or is the action simply necessary for a result? The answer helps you choose must, have to, or need to.
You must keep this door closed.
The speaker gives a firm instruction about the door.
A bus leaves at 6:15. Which form can explain why you must leave home early?
Use have to: I have to leave home early because the bus leaves at 6:15. The schedule creates the requirement.
Use must for a direct instruction
Use must when the speaker states a firm rule or feels a strong duty. It is common in clear instructions, notices, and formal rules. The verb after must stays in the base form for every subject.
Each student must write a name on the form.
Must makes writing a name a required action. Write does not change to writes.
I must remember to send the invoice today.
Here, the speaker feels a strong personal duty to send the invoice.
Use have to for rules and situations
Use have to when an outside fact makes an action necessary. The reason may be a workplace policy, an appointment time, a travel plan, or another practical situation. Change have to has to with he, she, or it.
The clinic has to confirm the appointment by Friday.
The deadline is outside the speaker, so has to fits the situation.
Which form completes this sentence: 'My brother ____ wear an ID badge at work'?
Use has to wear. My brother is singular, so have changes to has.
Use need to for a necessary step
Need to says that an action is necessary. It is useful when the sentence focuses on what must happen next. Like have to, it uses to before the base verb and changes to needs to with a singular subject.
We need to print the map before the signal disappears.
Printing the map is necessary because the signal may disappear.
The driver needs to check the fuel level.
Needs agrees with the singular subject the driver.
Keep the negative meanings separate
Must not means that an action is forbidden. Do not have to and do not need to mean that an action is unnecessary. These meanings can lead to opposite practical choices, so read the whole sentence before you answer.
You must not photograph the documents.
Taking photographs is prohibited.
You do not need to print the documents.
Printing is optional. The sentence does not prohibit it.
Which phrase tells a visitor that a coat is optional?
Use do not have to bring a coat. Must not bring a coat would prohibit the action.
Ask questions and talk about another time
Ask about a requirement with Do I have to ...? or Do I need to ...? For a past requirement, use had to with every subject. For a future requirement, use will have to. Must does not usually provide the past form in these ordinary obligation sentences.
Do we have to reserve a table?
The question asks whether making a reservation is required.
They had to wait outside during the repair.
Had to places the requirement in the past.
Before you go
Remember this
Choose must for a firm instruction or personal duty. Choose have to for an outside rule or situation. Choose need to for a necessary action. Check the negative carefully: must not means prohibited, while do not have to means optional. Use had to for a past requirement.
Practice with the written examples
You can practice with the written questions in the Learn tab. Each answer includes an explanation.
Try the written questionsListening test not available yet
This lesson does not have the recordings needed for a listening test. Use the written questions in the guide to check your understanding.
Try the written questionsQuestions about "Modal verbs for obligation: must, have to, and need to"
What is the difference between must and have to?
Must gives a firm instruction or a strong personal sense of duty. Have to often explains a requirement created by a rule, deadline, or situation. In many practical situations, both forms can express an obligation, but the context changes the emphasis.
I must call the landlord before noon.
When do I use need to?
Use need to when an action is necessary. It often focuses on the next practical step, as in You need to save the receipt for the return. Use needs to with he, she, or it, and put the base verb after to.
I have to call the landlord before noon because the office closes.
What does must not mean?
Must not means that an action is prohibited. You must not leave tools on the stairs means that leaving them there is not allowed. It does not mean that the action is merely unnecessary or optional.
Every guest has to sign the visitor log.
Is do not have to the same as must not?
No. Do not have to means that there is no need to do something, so the action is optional. Must not means that the action is forbidden. The difference matters because the two phrases can lead to opposite choices.
Every guest must sign the visitor log.
How do I talk about obligation in the past?
Use had to for an ordinary past requirement. Ravi had to reschedule the appointment last week describes something that was necessary then. Had to works with all subjects, including I, you, she, and they.
You need to save the receipt for the return.