1. Three messages about the same action
First decide what you want to say about the action. Must means it is necessary to do it. Mustn’t means it is not permitted. Don’t have to means there is no obligation to do it. These are three different messages, not interchangeable ways of saying the same thing.
Distinguish removing an obligation from imposing a prohibition. Choose don’t have to or don’t need to when an action is unnecessary, and mustn’t when it is forbidden. In the next three examples, the attendance rule changes even though the verb come stays the same.
You must come to the safety meeting.
You must come to the safety meeting.
Attendance is compulsory: missing the meeting would mean failing to meet the requirement.
You mustn't come into this room.
You mustn't come into this room.
This prohibits entry; it does not simply remove an obligation to enter.
You don't have to come to lunch. You're welcome if you want to.
You don't have to come to lunch. You're welcome if you want to.
There is no obligation. The invitation in the second sentence separately makes clear that coming is allowed.
2. Must: a requirement or strong necessity
Use must for a clear requirement or strong necessity. Speakers may remind themselves of an important task or state an organisation’s rule. Do not learn the absolute rule “must is only for personal decisions”: it is also natural in instructions.
After must, use the base form without to. Must does not change after he, she or it: she must wear, not she musts wear. If the main verb is be, it also stays be.
subject + must + base verb without to
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V1 / base form —
- The base verb without to: work, go, be.
I must charge my phone before I leave.
I must charge my phone before I leave.
The speaker considers the action necessary for their plan.
Every visitor must show a pass.
Every visitor must show a pass.
This requirement applies to every visitor. Show follows must without -s.
She must be ready at nine.
She must be ready at nine.
Use must + be. Add neither to nor is.
3. Mustn’t: it is necessary NOT to do something
Must not and mustn’t express prohibition in the rules in this lesson. The full form suits explicit written instructions, while the contraction is common in everyday conversation. Both are grammatically correct; the contraction does not change the meaning.
Don’t have to is not the negative counterpart of must when you mean prohibition. You mustn’t come is correct English if the person is forbidden to come. It simply does not mean that they may skip the event.
subject + must not / mustn’t + base verb without to
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V1 / base form —
- The base verb without to: work, go, be.
You must not share this door code.
You must not share this door code.
The rule prohibits sharing the code. It is neither advice nor an optional action.
We mustn't block the exit.
We mustn't block the exit.
The exit must remain clear. Use block after mustn’t.
4. Don’t have to and don’t need to: no necessity
Don’t have to removes an obligation; don’t need to says there is no need to do something. In the everyday situations here, the two often express the same practical message. If tools are already available, for example, bringing your own is unnecessary.
A lack of necessity is not, by itself, permission. You don’t need to use this door only says that using the door is unnecessary; it does not state all the access rules. When giving someone a choice matters, add explicit permission such as You can if you want, or use a context in which the action is clearly permitted.
Use don’t have to / don’t need to after I, you, we and they. Use doesn’t have to / doesn’t need to after he, she and it. After doesn’t, keep have and need, not has or needs.
subject + don’t / doesn’t + have to / need to + base verb
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V1 / base form —
- The base verb without to: work, go, be.
You don't need to bring tools. We provide them.
You don't need to bring tools. We provide them.
Tools are provided, so bringing your own is unnecessary. Nothing here states a prohibition.
Maya doesn't have to work on Friday.
Maya doesn't have to work on Friday.
There is no obligation. The sentence does not prove that Maya will definitely not work.
He doesn't need to print the form.
He doesn't need to print the form.
Doesn’t agrees with he. Need has no -s after it, and to comes before print.
5. Asking about necessity is different from asking permission
Do I have to …? and Do I need to …? ask whether an action is necessary. Start with Does for he, she and it. If the action is unnecessary, a natural reply is No, you don’t, or the full You don’t have to … / You don’t need to ….
Must I …? is also possible but sounds more formal. Do not add the auxiliary do to must. Do not answer No, you mustn’t if you only mean that an action is optional: that answer prohibits it.
Can I …? asks for permission. Being required to register, being permitted to register and being able to proceed without registration are different matters.
Do I need to book a seat? — No, you don't. There are plenty of seats.
Do I need to book a seat? — No, you don't. There are plenty of seats.
The question concerns whether booking is necessary, not whether booking is permitted.
Does he have to wear a badge? — Yes, he does.
Does he have to wear a badge? — Yes, he does.
Use have after does and repeat does in the short answer.
Must we leave now? — No, you don't have to leave yet.
Must we leave now? — No, you don't have to leave yet.
The reply removes the necessity to leave. Mustn’t leave would prohibit leaving.
6. The context must establish the relevant fact
Do not infer a rule from one isolated word. Free entry means entry costs nothing, but it does not guarantee that no ticket or reservation is needed. Organisers may issue free tickets that visitors must still show.
When a requirement is removed, do not automatically turn it into a prohibition. “A paper copy is no longer required” calls for don’t have to bring a paper copy. “Paper copies are not accepted and bringing them is forbidden” calls for mustn’t bring a paper copy.
In an open response, the facts and the intended message matter more than repeating a model exactly. Have to can express obligation, and don’t need to can express a lack of necessity. If an exercise specifically asks for must or don’t have to, use that form as part of the learning task.
Entry is free, but you must show your free ticket.
Entry is free, but you must show your free ticket.
The price does not remove the separate requirement to have a ticket.
You don't have to print the ticket. A ticket on your phone is fine.
You don't have to print the ticket. A ticket on your phone is fine.
Printing is unnecessary, but the ticket itself is still required.
7. Scope and your own message
Here we practise rules and necessity in present situations and for planned actions. We do not cover must for logical deduction, past obligations, or needn’t have done.
Before answering, check which action you are describing and whether it is required, forbidden or unnecessary. Make sure you have not added permission or claimed the action happened without evidence. Then check the form: must without to, but have to and need to with to.
Two or three sentences are enough for a short set of instructions. You can invent a workplace, course or event; no personal information is needed.
You must sign in. You mustn't enter the store room. You don't have to bring a laptop; we have computers here.
You must sign in. You mustn't enter the store room. You don't have to bring a laptop; we have computers here.
Each sentence has a separate purpose: requirement, prohibition and lack of necessity.
Common mistakes
Incorrect:She must to wear a badge.
Correct:She must wear a badge.
Use the base verb without to after must. Remove only the unnecessary to.
Incorrect:He mustn't uses this lift.
Correct:He mustn't use this lift.
Use the base form use after mustn’t, regardless of the subject he.
Incorrect:You don't has to pay.
Correct:You don't have to pay.
Use have after don’t. Has is not used in this construction.
Incorrect:She doesn't needs to wait.
Correct:She doesn't need to wait.
Doesn’t already marks the third person. Need follows it without -s.
Incorrect:We don't need bring chairs.
Correct:We don't need to bring chairs.
In don’t need to, to is required before the following verb.