Must & Have to – ESLnote Grammar

We use must and have to to talk about obligation, necessity, or strong advice. They are similar, but the source and tone of the obligation are a little different.

Quick Overview

Form	Core Meaning	Typical Source	Example
must + base verb	Strong personal obligation / rule; strong advice	Speaker / immediate situation	You must wear a helmet.
have to + base verb	External / general obligation; requirement	Law, policy, schedule, others	I have to pay my taxes.

1) Forms

Type	Structure	Example
Affirmative	subject + must / have to + base verb	You must finish this form. / We have to leave now.
Negative	subject + must not (mustn’t) + base verb subject + don’t/doesn’t have to + base verb	You mustn’t smoke here. (prohibited) You don’t have to come. (not necessary)
Questions	Must + subject + base verb…? Do/Does + subject + have to + base verb…?	Must we submit today? Do you have to work weekends?

2) Negative Meanings: Very Different!

Form	Meaning	Example
mustn’t	Prohibition (it is not allowed)	You mustn’t use your phone during the exam.
don’t/doesn’t have to	No obligation (it is not necessary)	You don’t have to attend the meeting.

3) Tense & Alternatives

must has no past form. For past necessity, use had to: I had to leave early yesterday.
For future necessity, both are fine: I must call her tomorrow. / I will have to call her tomorrow.
must and have to both use the base verb (no “to”). ❌ must to go → ✅ must go

4) Meanings in Use

A) Rules and obligations

Employees must display their ID badges.
Visitors have to sign in at the front desk.

B) Strong advice / personal requirement

You must see the dentist about that tooth.
I have to talk to my supervisor this afternoon.

C) Logical deduction (certainty)

We also use must to express a strong logical conclusion in the present.

The lights are off and the store is empty — it must be closed. (I’m sure.)

5) Forms at a Glance

Function	Natural Choice	Formality	Example
Everyday necessity	have to	neutral	I have to get up early.
Speaker-imposed rule / strong advice	must	slightly formal / emphatic	You must try this!
Past obligation	had to	—	She had to cancel.
No obligation (negative)	don’t/doesn’t have to	—	We don’t have to wear uniforms.
Prohibition (negative)	mustn’t	—	You mustn’t touch that.

6) Mini-Timelines

Present obligation:  You must / have to do it now → immediate necessity
Example: I have to submit the form today.

Past obligation:  had to → necessity in the past (action usually happened)
Example: We had to wait two hours yesterday.

7) Common Mistakes

❌ You must to wear a mask. → ✅ You must wear a mask.
❌ We don’t must pay. → ✅ We don’t have to pay. (no obligation)
❌ You mustn’t to park here. → ✅ You mustn’t park here.
❌ I musted leave early. → ✅ I had to leave early.

8) Quick Practice Prompts

Write two sentences about school rules (one with must, one with have to).
Rewrite: “It isn’t necessary to bring cash.” → Use don’t have to.
Give a logical deduction with must (present): The streets are wet → ?