subject + mustn't + base verbUse the same form with all subjects. After mustn't, the next verb is bare.
Mustn't vs Don't Have To
A2Use mustn't for prohibition: the action is not allowed. Use don't have to for lack of necessity: the action is optional.
What you'll learn
- Choose mustn't when a rule or warning bans an action.
- Choose don't have to when an action is optional.
- Build mustn't + base verb with all subjects.
- Build don't have to / doesn't have to + base verb correctly.
- Tell the difference between not allowed and not necessary.
Structure
subject + don't/doesn't + have to + base verbUse don't with I, you, we, they and doesn't with he, she, it. Keep have, not has.
Build a sentence
Subject
Verb
Youmustn'tpark here
You mustn't park here.
Choose mustn't when a rule or sign bans the action.
When to use
Rules and signs
Use mustn't for bans from signs, laws, school rules, workplace rules, and direct warnings. You mustn't park here.
Strong warnings
Use mustn't when a person says an action is dangerous or unacceptable. You mustn't touch that wire.
Optional actions
Use don't have to when doing something is your choice. You don't have to come early if you don't want to.
No need now
Use don't have to when the reason is already solved. Maria doesn't have to buy coffee because Tom already bought some.
Markers
not allowedforbiddenrulesignoptionalno needalreadyif you want
In contrast
vs have-to-external-obligation
Have to says necessity or obligation. Don't have to removes that necessity; mustn't changes the meaning to prohibition.
vs must-strong-obligation
Must says a strong obligation. Mustn't is the negative of permission here: not allowed, not just not necessary.
Common mistakes
Wrong
You don't have to use your phone during the exam.
Correct
You mustn't use your phone during the exam.
The exam rule bans the action. Don't have to means it is optional, not forbidden.
Wrong
You mustn't print the ticket. The hotel accepts the email on your phone.
Correct
You don't have to print the ticket. The hotel accepts the email on your phone.
Printing is unnecessary, but it is still allowed. Mustn't would mean printing is prohibited.
Wrong
Lisa mustn't to leave early.
Correct
Lisa mustn't leave early.
After mustn't, use the base verb with no to.
Wrong
Maria doesn't has to drive today.
Correct
Maria doesn't have to drive today.
After doesn't, use have, not has.
Wrong
He don't have to wear a tie.
Correct
He doesn't have to wear a tie.
With he, she, it, use doesn't have to.
Common misconceptions
❝ Mustn't and don't have to are both negatives, so they mean the same thing. ❞
They are different. Mustn't means the action is banned; don't have to means the action is optional.
❝ Mustn't is just a softer way to say don't have to. ❞
No. Mustn't is stronger because it blocks the action completely.
Skills in this rule (6)
USE_MUSTNT_FOR_PROHIBITIONw5Use mustn't to say something is not allowed
Use mustn't when a rule, sign, instruction, or strong warning says an action is prohibited. The meaning is no permission, not no need.
USE_DONT_HAVE_TO_FOR_NO_NEEDw5Use don't have to to say something is not necessary
Use don't have to when the action is optional. The person can do it, but there is no need.
FORM_MUSTNT_PLUS_BASE_VERBw4Build sentences with mustn't + base verb
After mustn't, use the base verb with no to and no verb ending. The form stays the same for all subjects.
FORM_DONT_DOESNT_HAVE_TOw5Build sentences with don't have to / doesn't have to + base verb
Use don't have to with I, you, we, they and doesn't have to with he, she, it. The main verb stays in the base form.
PICK_RULE_AND_OPTIONAL_MARKERSw3Recognize clues for prohibition and no need
Words like not allowed, forbidden, rule, and sign point to mustn't. Words like optional, no need, already done, and no problem point to don't have to.
EXPLAIN_THE_DIFFERENCEw4Tell the difference between not allowed and not necessary
Choose mustn't for a ban and don't have to for no need. The action is impossible in one case and optional in the other.