- OBLIGATION/NECESSITY: have to / must + infinitive
|- More common for general, external obligations (rules and laws). |- More common for specific or personal obligations.|
|I have to wear a shirt and a tie at work. (it’s the rule in this company) |I must buy a newshirt because this one is very old. (it’s my own decision) |
|It’s a normal verb and it exists in all tenses.|- It’s a modal verb. The only forms are MUST and MUSTN’T. |
|I had to wear a uniform at my primary school.| |
|You have to wear a seatbelt in a car....