must

must — modal verb

1. Describes a situation where a rule, a law, or a practical need requires somethin

1.modal verbA2
Definition

Describes a situation where a rule, a law, or a practical need requires something — for example, fastening a seatbelt because the law demands it, or sending a form before a closing date.

Example

All passengers must fasten their seat belts during takeoff and landing.

must + base verb — rule or law obligation

Felix must finish his homework before he can watch television.

Common collocations
  • must by law
  • must by regulation
  • must absolutely
  • must simply
Synonyms
  • have to

    more common in everyday speech for describing obligations; works in all tenses

  • need to

    slightly weaker than 'must', focuses on what is necessary rather than what is required by rule

  • be required to

    more formal; common in official notices and regulations

Antonyms
  • must not

    the direct negative — forbids the action

  • do not have to

    indicates that something is not necessary, not that it is forbidden

Grammar Patterns

must + base verb

must not + base verb (prohibition)

must + be + past participle (passive obligation)

Usage Note

Must has no past-tense form. For past obligation, use 'had to' (e.g., 'I had to leave early yesterday'). For prohibition in the past, use 'was / were not allowed to' (e.g., 'We were not allowed to park there'). Must is also not used with 'do/does/did' in questions or negatives — the negative is must not (contracted mustn't).

Common Mistakes

I must go to the store yesterday.
I had to go to the store yesterday.
'must' has no past tense; use 'had to' for past obligation.
You must not go to the party if you do not want to.
You do not have to go to the party if you do not want to.
'must not' means it is forbidden, not merely unnecessary; use 'do not have to' for optional things.

2. used to show that you have made a strong decision to do something and will not l

2.modal verbB1
Definition

used to show that you have made a strong decision to do something and will not let anything stop you — for example, promising yourself to quit smoking or to save money each month.

Example

I must call my grandmother more often — I keep forgetting.

must + base verb — self-imposed personal intention

Christopher must stop staying up so late or his health will suffer.

Common collocations
  • must...or
  • must remember to
  • must make sure
Synonyms
  • have got to

    more informal; common in British English for personal intentions

  • be determined to

    conveys the same strong resolve but works in all tenses

  • will

    less forceful; a simple statement of future action rather than a strong intention

Grammar Patterns

must + base verb

Usage Note

This sense expresses a personal resolve, not an external obligation. For past intentions, use 'was determined to' (e.g., 'I was determined to finish the marathon').

3. used before a verb to make your statement feel more forceful or emotionally char

3.modal verbB1
Definition

used before a verb to make your statement feel more forceful or emotionally charged — for example, insisting that something is true, expressing surprise, or adding weight to an opinion.

Example

I must say, I am really impressed by your presentation.

must say — fixed emphatic phrase for emotional force

I must admit, I was completely wrong about the election result.

must admit / must say — fixed emphatic phrase

Common collocations
  • must admit
  • must say
  • must understand
Synonyms
  • really

    adverb that can add similar force: 'You really should see the sunset'

  • simply must

    more emphatic version of 'must'

Grammar Patterns

must + base verb

must admit / must say

must + be + complement

Usage Note

Distinguish from sense 5 (LOGICAL DEDUCTION): in this emphasis sense, 'must' adds emotional force to a statement the speaker already knows to be true, rather than drawing a conclusion from evidence. Common fixed phrases include 'I must say', 'I must admit', and 'you must know'.

4. used to tell someone that you strongly believe they will enjoy or benefit from s

4.modal verbA2
Definition

used to tell someone that you strongly believe they will enjoy or benefit from something — for example, suggesting a film, a restaurant, or an experience with enthusiasm.

Example

You must try the chocolate cake at that little café downtown.

must + base verb — enthusiastic suggestion

Adina told me, 'You must read this novel — you will love it.'

Common collocations
  • must try
  • must go
  • must see
  • must visit
Synonyms
  • should

    less forceful than 'must'; a gentle suggestion rather than an enthusiastic recommendation

  • have to

    usually implies obligation, not recommendation; less suitable for enthusiastic suggestions

  • ought to

    similar to 'should' in strength; slightly more formal

Grammar Patterns

must + base verb

Usage Note

This sense is only used in the second person ('you must...') or reported speech about a recommendation ('She said I must...'). Unlike sense 1 (NECESSITY), there is no external rule — the speaker is simply expressing personal enthusiasm.

Common Mistakes

You must go to the museum — it is required for the class.' (if the speaker means a class requirement, not a recommendation).
You must go to the museum
it is fantastic.' — For requirements, the context should clearly show a rule; for enthusiastic suggestions, the context should show personal enjoyment.

5. Expresses near-certainty based on clear evidence — for example, hearing a doorbe

5.modal verbB1
Definition

Expresses near-certainty based on clear evidence — for example, hearing a doorbell and concluding a guest has arrived, or seeing wet ground and deciding it rained.

Example

The kitchen light is on, so Mateo must be home by now.

must + base verb — logical conclusion from visible evidence

You have been walking all day — your feet must hurt.

Common collocations
  • must be
  • must have
  • must have been
Synonyms
  • have to

    can express certainty: 'That has to be the right answer.'

  • be bound to

    slightly more formal; emphasises inevitability: 'She is bound to be tired after the trip.'

  • can only be

    used when only one explanation fits: 'It can only be him.'

Antonyms
  • cannot / can't

    the logical negative — expresses certainty that something is NOT true

Grammar Patterns

must + base verb (present deduction)

must have + past participle (past deduction)

must be + adjective/noun

Usage Note

For past deduction, use 'must have + past participle' (e.g., 'She must have left the key on the table'). The negative of this sense is 'cannot / can't + base verb' or 'cannot / can't have + past participle' (e.g., 'He cannot be at work — his car is still in the driveway'), NOT 'must not', which expresses prohibition, not logical impossibility.

Common Mistakes

He must not be at home — his car is there.
He cannot be at home
his car is there.' — 'must not' means prohibition; use 'cannot / can't' for logical impossibility.
She must be left already.
She must have left already.
For past deduction, use 'must have + past participle', not 'must be + past participle'.
Idioms

if you must (do something)

idiom

You say this when you agree to let someone do something, but you are not happy about it.

Dad said I could go to the party if I must.

If you must know, I bought the dress for the wedding.

must-see/must-read/must-have, etc.

idiom

Something that is so good or important that everyone should see, read, or own it.

The new museum exhibit is a must-see for art lovers.

This cookbook is a must-have for anyone who loves Italian food.

needs must (when the Devil drives)

idiom

You say this when you have to do something unpleasant because there is no other choice.

I hate cleaning, but needs must when the Devil drives.

She took the night shift because needs must; she needed the money.

must — noun

must — prefix

Word family

  • must-see
    adjective / nounB1
  • must-read
    adjective / nounB1
  • must-have
    adjective / nounB1

Synonym discussion

Sense: modal verb/1

Must expresses the strongest obligation of these five words. It is used for rules and laws ('Students must wear uniforms') or personal determination. Have to overlaps with must for external obligations but is more flexible — it works in all tenses ('I had to leave early'), while must has no past form. Need to is slightly weaker than must; it focuses on what is practically necessary rather than what is demanded by authority. Should and ought to express advice or moral duty rather than firm obligation — if you say 'You should apologize,' the other person could still refuse, but 'You must apologize' leaves no room for choice. In everyday speech, should is the most common for suggestions, while must is reserved for stronger contexts.

must ↗have toshould ↗need toought to

Common collocations

Nouns

Adverbs

Phrases

  • must have
  • must be
  • must not

Prepositions

Etymology

Proto-GermanicOld EnglishMiddle EnglishEnglish

Must comes from Old English 'mōste', which was the past tense of 'mōtan' — a verb meaning 'to be allowed' or 'to have to'. Over time, the past-tense form replaced the original present tense, while the original present tense of 'mōtan' developed separately into the modern word 'may'. This is why 'must' has no present-tense third-person form (*musts) and no past tense — it is historically a past form that took over present meaning. The noun sense ('a must', meaning an essential item) emerged much later, in the early 20th century.