Ingles

Expressing obligation
When it is necessary or obligatory to do something, you express obligation.
Obligation in the present:
I have to finish my work before this evening.
I have got to learnEnglish if I want to live in the USA.
I must see the doctor soon because I don't feel well.
It is obligatory/compulsory that I stop when the traffic lights turn red.
It is necessary that I take ataxi. I'm late.
Obligation in the past:
I had to work extra hours to pay my bills.
Obligation in the future:
I'll have to borrow money.
Things to remember:
1. The difference between "Have to"and "must" is that "have to” indicates that someone else has imposed conditions on us.
2. The simple past of "must" is "had to".
3. The simple future of "must" is "will have to".
4. Should alsoexpresses obligation. But there is a difference between must / have to and should:
must / have to = 100% obligation. "When the traffic light turns red, you must stop."
should = 50% obligation. It's morean advice than an obligation. “You look tired. You should have a rest."
Dialogue:
Policeman:
Don't you know that you must stop when the traffic lights are red?
Driver:
Sorry sir. I was soabsent-minded that I didn't pay attention to the traffic lights.
Policeman:
Well sir, you'll have to pay a fine!


Expressing lack of necessity (Absence of obligation)
To express lack ofnecessity (also called absence of obligation), speakers usually use "don't have to", don't need to", "needn't”.
The form that we use to express lack of necessity could be one of the following:
He doesn'thave to get up early.
He doesn't need to get up early.
He needn't get up early
Expressing lack of necessity in the present:
I don't
have
to take my umbrella. It isn't raining

need

Ineedn't
take my umbrella. It isn't raining
I don't have to drive fast.
I don't need to write the report myself. My secretary can do that for me.
I needn't buy all these things.
It isn't...