ESL Vietnam Zone

“Have/has to” and “don’t have/has to” – The simplified rules

• Being a modal verb, “have/has to” is followed by a verb in base form and it says that something is necessary.

Examples:
I have to ride the bike three hours a day.
My daughter has to study English every day.

• To say there is no obligation or something is not necessary, use “don’t/doesn’t have to” followed by base form.

Examples:
We don’t have to wear uniform at school in Romania
His wife doesn’t have to work, she is rich.

• Of course do/does is used for forming questions and negatives.

Examples
Why do you have to study English?
Does she have to work on Sunday?

“must”, “must not” and “can’t” – the simplified rules

• “must” is followed by a verb in base form and express strong obligations and rules

Example:
The traffic sign says: “all motorcycles must turn left”.

• Use “must not” or “can’t” to say something is prohibited.

Examples:
You must not leave your luggage unattended in the airport.
You can’t bring food into this cinema.

• To form questions you should use “have to” (it is more popular than “must”)

Example:
Do I have to buy a ticket?

Additional notes

• ‘Must’ and ‘have to’ are very similar but ‘have to’ seems to be more common in speaking. I find ‘must’ fulfilled with obligations (it is more used in official forms, notices and probably in the army.
• The other side, their negations ‘must not’ and ‘don’t have/has to’ have completely different meaning (You don’t have to go vs. You must not go).
• ‘Can’t’ and ‘must’ have similar meaning but ‘can’t’ is more common in speaking.
• The words ‘can’t', ‘must’ and ‘must not’ are the same for all persons.