12th May ; Live Microsoft Teams ! Good Friends ! Obligation ; Necessity ; Prohibition

must / have to

Must and have to are used to express obligation. When we use must this usually means that the obligations comes from the speaker, it’s like a personal obligation, whereas have to normally means that the obligation is external.

• I must give up smoking. (I need to, I say so)
• I have to give up smoking. (I’m obliged. My doctor says so)

mustn’t / don’t have to

The negative forms mustn’t and don’t have to are completely different. Mustn’t is used to express prohibition (an obligation not to do something), whereas don’t have to is used to express an absence of obligation. 

• You mustn’t reveal where you get the information. (=you have the obligation not to do it)
• You don’t have to arrive before 7. (=you can do it, but it’s not necessary, there’s no obligation)

Source : https://test-english.com/explanation/b2/modal-verbs-permission-obligation-prohibition-necessity/

 Let's practice : 

https://test-english.com/grammar-points/a2/have-to-dont-have-to-must-mustnt/

Manual digital : https://manuale.edu.ro/manuale/Clasa%20a%20VII-a/Limba%20moderna%20engleza/U0MgR1JVUCBFRElUT1JJ/
Ex pages 98 and 99