1. MODALS OF OBLIGATION
Must, have to,
don’t have to, mustn’t

2. MODALS OF OBLIGATION AFFIRMATIVE USE EXAMPLES MUST + base form
When the obligation is personal
To strongly recommend or offer something
I must finish my homework before I go out.
You must study for the exam.
HAVE TO
(HAS TO)
To talk about a rule for us made by somebody else
We have to take our shoes off in the gym.
HAD TO
WILL HAVE TO
HAVE (HAS) HAD TO
To talk about things that are necessary because of the circumstances
She will have to go to the dentist if she’s got a toothache.
I didn’t go out last night because I had to look after my brother.
Paul has had to walk home because she missed the bus.

3. MODALS OF OBLIGATION NEGATIVE USE EXAMPLES MUSTN’T + base form
Prohibition
When it is necessary NOT to do something
You mustn’t talk during the exam.
You mustn’t forget to bring your gym kit tomorrow.
DON’T HAVE TO
DOESN’T HAVE TO
Something is not necessary to do
Lack of obligation
You don’t have to bring a present for my birthday.
You don’t have to go if you don’t want.

4. MODALS OF OBLIGATION REFERENCES PRESENT PAST FUTURE PRESENT PERFECT
MUST
-----
HAVE TO
HAD TO
WILL HAVE TO
HAVE HAD TO
DON’T HAVE TO
DIDN’T HAVE TO
----