EF 7C: Overview: Difference Between „Have to“, „Don’t Have to“, „Must“, and „Mustn’t“

Here is a comparison of these four common expressions used to describe obligation, prohibition, or lack of necessity:

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Expression	Usage	Meaning	Example	Translation
Have to	Expresses obligation (something is necessary, often due to external rules).	Must	You have to wear a helmet.	Musíš nosit helmu.
Don’t Have to	Expresses lack of necessity (you can do it, but it’s not required).	Don’t need to	You don’t have to wear a tie.	Nemusíš nosit kravatu.
Must	Expresses strong obligation (often personal or urgent).	Must	You must finish your homework.	Musíš dokončit svůj domácí úkol.
Mustn’t	Expresses prohibition (something is strictly not allowed).	Must not	You mustn’t park here.	Nesmíš tady parkovat.

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Differences Between These Expressions

1. Obligation vs. Lack of Obligation:
   • Have to: Indicates obligation, often imposed by external factors (e.g., rules, laws).
   • Must: Indicates obligation, often personal or moral.
   • Don’t have to: Indicates something is not obligatory, and you have a choice.
   • Mustn’t: Indicates prohibition, something is strictly not allowed.
2. Source of Obligation:
   • Have to: External reason (e.g., rules, law).
   • Must: Internal reason (e.g., personal belief, recommendation).
3. Time Usage:
   • Have to/Don’t have to: Can be used for present, past, and future:
     • Present: I have to go. [Musím jít.]
     • Past: I had to go. [Musel jsem jít.]
     • Future: I will have to go. [Budu muset jít.]
   • Must/Mustn’t: Cannot be used for past or future. For past and future, other expressions are used:
     • Past: Had to (e.g., „I had to go.“)
     • Future: Will have to (e.g., „I will have to go.“)
4. Negatives:
   • Don’t have to: Does not express prohibition, only lack of necessity.
   • Mustn’t: Expresses strict prohibition (you are not allowed to do something).

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Examples for Comparison

1. Have to:
   • You have to pay your taxes. [Musíš zaplatit daně.]
2. Don’t Have to:
   • You don’t have to come if you’re busy. [Nemusíš přijít, pokud máš hodně práce.]
3. Must:
   • You must call your mother. [Musíš zavolat své matce.]
4. Mustn’t:
   • You mustn’t use your phone during the exam. [Nesmíš používat telefon během zkoušky.]

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Summary

• „Have to“ and „must“ both express obligation, but „must“ is generally stronger or more personal.
• „Don’t have to“ means something is not necessary, while „mustn’t“ means something is prohibited.