This document discusses the differences between should, must, and have to. Should is used to give advice or polite obligations, while must and have to indicate strong obligations. Should expresses recommendations, while must and have to convey convictions. Must refers to personal circumstances requiring obligation, and have to refers to external circumstances necessitating obligation. Mustn't and don't have to are the negative forms, with mustn't prohibiting actions and don't have to indicating an absence of necessity.

1. Should, must, have to

2. Should
 Should + infinitive (without to): You should eat
more fruit
 Negative form: You shouldn’t smoke
 Question form: Should I give her a present?
(asking for advice)
 Verb tenses: past, present, future:
 I should have finished my report yesterday (past –
always REGRETTING)
 You should help me, I can not do it alone (present)
 Tomorrow you should call your parents (future)

3. Should
 Used for giving advice: something is good, so
you should do it. It is a RECOMMENDATION, not
an obligation:
If you feel bad you should go to the doctor
 Obligation, but in a very polite way. Something
you should do, but it is not a repressive order:
Anyone who wants to enter the conference should
show his credentials

4. Must/ Have to
 Strong OBLIGATION, not a recommendation:
You must come here immediately
If you want to make a career in a company you
have to speak English (there is no other
possibility)
 Conviction of something that is going to
We should buy a new car (it is a desire; maybe we
do it, maybe we don’t)
We must buy a new car (we will do it, it is almost
sure)

5. Must/ Have to
 MUST: personal circumstance makes the obligation
necessary
I must go to bed earlier.
They must do something about it.
You must come and see us some time.
 HAVE TO: some external circumstance makes the
obligation necessary.
I have to arrive at work at 9 sharp. My boss is very
strict.
We have to give him our answer today or lose out on
the contract.
You have to pass your exams or the university will not
accept you.

6. Mustn’t/ Don’t have to
 MUSTN’T: prohibitions; something is forbidden. We
CAN’T do it:
We mustn't talk about it. It's confidential.
I mustn't eat chocolate. It's bad for me.
You mustn't phone me at work. We aren't allowed personal calls.
 DON’T HAVE TO: absence of necessity. It is not
necessary; there is no obligation
We don't have to get there on time. The boss is away
today.
I don't have to listen to this. I'm leaving.
You don't have to come if you don't want to.