"MUST" OR "HAVE TO"

"MUST" OR "HAVE TO"
Some people, even I, get mixed up with "must" and "have to". Therefore, I will show you the differences when using them.

MUST: 
- To show the speaker's really certain about something. Based on clear evidence, the speaker is making a logical deduction.
- To express a strong obligation. Some personal circumstance makes the obligation necessary.

E.g. Look at you, you're covered in sweat. You must be hot! (Logical deduction)
E.g. I must go to bed early or else when I wake up, I will be tired.

HAVE TO: 
- Also to express a strong obligation, but it is necessary due to some external circumstance.

E.g. My teacher is very strict. I have to go to school on time.
E.g. You have to work hard in order to pass the final exam.

MORE: 
"Have got to" means the same as "have to".

We can also use ' will have to' to talk about strong obligations. Like 'must' this usually means that that some personal circumstance makes the obligation necessary. (Remember that 'will' is often used to show 'willingness'.)

E.g. I will have to speak to their parents.