Must: the speaker's own obligation

Must shows that the speaker personally thinks something is necessary. We use it for our own decisions (I must…), for orders and strong advice (You must…), and for warm invitations.

subject + must + base verb (no to, no -s)

• I must apologise to her — I was really rude yesterday.
• You must read this book — you'll love it.
• He must learn to listen to other people.

Have to: a requirement from outside

Have to shows that the obligation does not come from the speaker: there is a law, a company policy, a rule of the house, or the situation leaves no choice. The speaker simply reports the requirement.

• I, you, we, they → have to wait
• he, she, it → has to wait
• past → had to wait
• future → will have to wait
• question → Do / Does … have to wait?

• In this country you have to carry your ID with you.
• My flatmate has to start work at six, so he goes to bed early.
• Do we have to take off our shoes at the door?