Must - have to - should

1. MODALS OF OBLIGATION
MODAL VERBS

2. What are MODAL VERBS?
• HE MUST TOMORROW
• They are auxiliary verbs, they go with other
verbs

3. What are MODAL VERBS?
• HE CAN WILL MEET YOU
• 2 modals verbs cannot go together
• HE MUST TO MEET YOU
TOMORROW
• Followed by infinitive without “to”, except
modal verb HAVE TO.

4. What are MODAL VERBS?
• HE CANS MEET YOU
• Don’t have 3rd person “-s”
• LAST YEAR I CANNED
• Don’t have endings like -ed, -ing, etc

5. MUST & HAVE TO
• I must finish my homework before 8
• We have to start work at 9 am
They are both used to express that something
is necessary

6. MUST
• I must find a hotel to stay at tonight
• The speaker decides that something is
necessary (INTERNAL decision)

7. HAVE TO
• I have to wear a uniform
• Somebody else has made the decision,
it’s not the speaker’s opinion
(EXTERNAL decision)

8. OTHER TENSES
• MUST: past & future with HAVE TO
• When I was young, we had to wear a
uniform at school
• Next year you will have to study harder

9. MUSTN’T & DON’T HAVE TO
• Very different meanings in negative:
• You mustn’t open the door
• You don’t have to open the door

10. MUSTN’T
• You mustn’t open the door. Lately there
have been many robberies in the
neighbourhood.
• (It’s forbidden /prohibited)
• =can’t/be not allowed to

11. DON’T HAVE TO
• You don’t have to open the door. I have
the keys.
• (It’s not necessary)

12. SHOULD / SHOULDN’T
• I think you should see the doctor
• I think you shouldn’t watch so much TV
• =ought to/ought not to
• Give an opinion about what’s the best thing
do do.
• Not as strong as MUST /HAVE TO:
• You must see the doctor
• You have to see the doctor (You have no
alternative, strong recommendation)