1. When an action is truly necessary
Must can express strong necessity or obligation. The speaker does more than name a good idea: they emphasise that the action is important and required.
Must itself does not mean the action has already been performed. I must send the email means the email needs sending, rather than that it has already been sent.
Subject + must + 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.
I must send the email today.
I must send the email today.
The speaker names a necessary task and its deadline.
We must find the key.
We must find the key.
The obligation applies to the speaker together with others.
2. After must: no to, no -s
The base form is the verb without additional endings: go, write, take, be, have. Use it after must: must go, must be, must have.
Must does not change with person or number: I must, she must, everyone must, they must. Do not add -s to either must or the following verb.
In must have a key, have means possession. This simple construction is appropriate for an obligation to have a key; not every sequence beginning with must have is a complex tense construction.
Nora must bring her notebook.
Nora must bring her notebook.
After must, use bring, rather than brings or to bring.
Each guest must have a ticket.
Each guest must have a ticket.
At this fictional event, this is a requirement for a guest; have does not become has.
You must be ready at ten.
You must be ready at ten.
After must, use be, rather than am, is or are.
3. A personal need and a public rule
I must often expresses a strong personal decision. Must is also natural in rules and notices: the requirement may concern visitors, participants or employees.
Have to also expresses necessity. The distinction “must comes from the speaker, have to from external circumstances” is a common tendency, rather than a rigid ban. Both forms can describe the same rule.
All club, studio and event rules in this lesson are invented for language practice. They do not state real laws or safety instructions.
I must sort these papers.
I must sort these papers.
The speaker personally emphasises the necessary action.
Visitors must use the side door.
Visitors must use the side door.
A possible notice in a fictional club. Visitors have to use the side door can also express this requirement.
4. A strong requirement is different from advice
Compare must and should in ordinary advice about an action. Must usually sounds stronger; should more gently suggests what is advisable. Both forms can be grammatical.
You must can sometimes sound authoritative. With a colleague or friend, consider the purpose and relationship: a strong requirement is not appropriate in every situation.
Mustn’t means prohibition, while don’t have to means absence of necessity. This briefly marks the topic’s boundary: our main focus is a positive statement of what needs doing.
You must check the number.
You must check the number.
A strong requirement to perform the check.
You should check the number.
You should check the number.
Grammatical advice with a different strength, rather than an incorrect must.
You don't have to bring a cup.
You don't have to bring a cup.
There is a choice. This does not prohibit bringing a cup.
5. Clarifying an obligation
In a question, put must before the subject. Do not add do or does to must.
Must I…? and Must we…? are grammatical, but can sound formal or insistent, sometimes expressing annoyance. Neutral Do I have to…? is often more convenient in everyday conversation.
When an exercise specifically requests a question with Must, practise that form. Another grammatical way to ask is not an English error, although it does not meet the specified structure.
Must + subject + 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.
Must we bring our own chairs?
Must we bring our own chairs?
Must comes before we; bring does not change form.
Do we have to bring our own chairs?
Do we have to bring our own chairs?
A natural conversational alternative; a different construction.
6. Now, tomorrow and yesterday
Must can concern a necessary action in the present or future. Tomorrow does not require will before must. Standard English does not use will must.
For an ordinary account of past obligation, use had to. There is no form musted.
Do not turn this advice into an absolute claim that must is impossible in a past narrative. In reporting someone’s words or thoughts, must is sometimes retained, particularly when the action was still ahead. Full tense backshift is a separate topic.
I must call the office tomorrow.
I must call the office tomorrow.
A future action with must, without will.
Yesterday I had to wait outside.
Yesterday I had to wait outside.
An ordinary past obligation is expressed with had to.
She said she must leave soon.
She said she must leave soon.
This version is possible in reported speech: leaving was still ahead relative to the moment of her words.
7. Not every must expresses obligation
Context determines the meaning. Must can express a deduction or strengthen a friendly invitation. Seeing must alone is insufficient to identify a sentence as a rule.
These examples only help recognise the boundaries of this lesson. We do not practise complex deductions about the past, perfect constructions or different types of modality here.
For your own answers, the model is one alternative. Check the meaning, must + base verb and compliance with the visible task instruction. Allow natural synonyms if they do not change facts or the required strength.
The lights are on. Someone must be home.
The lights are on. Someone must be home.
A deduction from evidence, rather than a requirement to be at home.
You must come for tea sometime.
You must come for tea sometime.
In a friendly context, this is a warm invitation, rather than a compulsory rule.
Common mistakes
Incorrect:She must to bring the key.
Correct:She must bring the key.
The verb after must has no to.
Incorrect:He musts call the office.
Correct:He must call the office.
Must does not take -s with he.
Incorrect:Everyone must writes a name.
Correct:Everyone must write a name.
After must, use base write, even with everyone.
Incorrect:Do I must wait here?
Correct:Must I wait here?
Must itself goes before the subject in a question; no do is added.
Incorrect:We will must leave tomorrow.
Correct:We must leave tomorrow.
Do not put will and must together. Must can already concern tomorrow’s action.