Modal Verb MUST

Modal Verb MUST — Meaning, Use & Examples

Hello, dear English learners! Welcome to a new grammar lesson from My Lingua Academy, where we help you strengthen your English skills step by step. Today, we’re going to explore one of the modal verb must.

You’ll learn how and when to use it, how it differs from have to, and what common mistakes to avoid.

What Does “Must” Mean?

We use must to show that something is necessary, important, or required by law, rules, or personal obligation.

• You must water this plant regularly to prevent it from wilting.
• You must answer all the questions on the test.
• The gate must be locked after ten o’clock.

Tip: “Must” expresses strong necessity or personal obligation, often from the speaker’s point of view.

Negative Form — Mustn’t / Must Not

We use mustn’t (or must not) to say that something is forbidden or not allowed.

• You mustn’t shout when your brother is sleeping.
• The things in the museum must not be touched.
• We mustn’t forget how much we owe to our parents.

Tip: “Mustn’t” does not mean “don’t have to”!

 (“Don’t have to” means “it isn’t necessary”, not “it’s forbidden.”)

You mustn’t park here. (= It’s not allowed.)

You don’t have to park here. (= It’s not necessary; you can, but you don’t need to.)

Expressing Certainty with Must

We use must when we’re sure or almost certain that something is true.

• Their house must be worth a fortune — it’s huge!
• You’ve been working all day; you must be tired.
• I can’t see Simon; he must be at home. 

Tip: This use of “must” expresses a logical conclusion based on evidence. Modal Verb MUST

Making Recommendations with Must

We can also use must to strongly recommend something to someone.

• You must come and visit us sometime!
• That dress looks amazing on you — you must buy it.
• You must watch that film; it’s brilliant!

Tip: This use of “must” is very common in friendly advice or suggestions.

“A Must” and Related Expressions

We can use “a must” as a noun to talk about something essential.

• Good-quality boots are a must if you go hiking in the mountains.
• If you want to learn English well, a good online dictionary is a must.

We can also use must-see, must-have, must-read, must-watch, etc.

• This bag is a must-have!
• The new film with Robert Carlyle is a must-watch.
• That book is a must-read for anyone learning English. Modal Verb MUST

Must vs Have to

We use must mainly in the present tense, while have to can be used in all tenses (past, present, and future).

• Ann had to work overtime yesterday. (past)
• Do I have to wear a uniform? (present)
• Will we have to take our shoes off? (future)
• Their colleague is on holiday, so they’ve had to take on her job as well. (present perfect)

Tip:

Use must for personal rules or strong recommendations.

Use have to for general rules or external obligations.

• You must study harder if you want to pass.. (speaker’s opinion)
• You have to wear a seatbelt. (law or rule)

Common Mistakes with “Must”

🚫 Wrong: Susan must to do her homework.

✅ Right: Susan must do her homework.

Never use to after must.

Referring to the Past — Must have + Past Participle

When we want to express certainty about the past, we use must have + past participle.

• They aren’t at home — they must have gone out.
• The thieves must have entered through the bathroom window.
• I must have left my phone in that café where we stopped for coffee.

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