EXPLANATION OF SHOUD, MUST, HAVE TO

Should / must

Should  / must

1) Should  

 is used to give advice ,to make recommendations or to talk about what we think is right or wrong.

 positive form ; shoulde.g. :
You should eat more slowly. 
 negative form  :shouldn't
e.g.
  You shouldn't work so much.

2) must

 is used to talk about an obligation or  probability .

positive form : must
e.g.
You must do your homework .
negative  form : mustn't

 is used  to forbid something ,it is forbidden, it is foolish to do it.

 e.g.
You mustn't smoke in hospitals.

HAVE TO

Have to / Has to = it is necessary 
Don't have to / Doesn't have to = it isn't necessary

AFFIRMATIVE SENTENCES	SUBJECT	MODAL	VERB	EXAMPLES
affirmative sentences ( + )NECESSITY:  have to/has to  means it is necessary.	I you we they	have to	clean get pick up have eat go work	I have to clean my room. You have to get a new book. We have to pick up the laundry. They have to have a notebook.
	he she it	has to		He has to eat dinner now. She has to go to work now. It has to work.
NEGATIVE SENTENCES	SUBJECT	MODAL	VERB	EXAMPLES
negative sentences ( - )LACK OF NECESSITY:  don't have to/doesn't have to  means it is not necessary.  You have a choice.	I you we they	don't have to	work do clean eat work go be	I don't have to work on Saturday. You don't have to do that. We don't have to clean the car. They don't have to eat pizza.
	he she it	doesn't have to		He doesn't have to work tomorrow. She doesn't have to go today. It doesn't have to be that way.
QUESTIONS	DO	SUBJECT	MODAL	VERB	EXAMPLES
questions ( ? )	Do	I you we they	have to	clean get pick up have eat go work	Do I have to clean my room? Do you have to get a new book? Do we have to pick up the laundry? Do they have to have a notebook?
	Does	he she it			Does he have to eat dinner now? Does she have to go to work now? Does it have to work?