Must
Usamos must o have to para decir que algo es necesario. Must y have to tienen significados muy similares en su forma positiva, sin embargo, have to es más común de lo que se debe.
must: In general, it expresses what the speaker thinks is necessary.
Examples:
- I must stop smoking.
- We must go, it's already midnight.
- They must work harder.
Have to
in general, it suggests that somebody else has imposed the decision.
- Tom has to wear a uniform at school.
Examples:
- I had to go to three meetings yesterday.
- I had to do my homework.
Muy importante: No podemos usar must en el pasado, para decir que algo era necesario en el pasado, usamos had to.