ملخص الدرس / الأولى ثانوي/اللغة الإنجليزية/Grammar/Need to- have to- had to- must

Must:

Forms:

possitive	Negative	Interrogative
I/you/he/she/we/they must go now	I/you/he/she/we/they must not/ musn't go now	must I/he go now when must I/you... go?

Must= obligation 

we use must when we think it is important or essential to do an action .

In England ,you must drive on the left, but in Algeria, you must drive on the right .

Musn't= negative of obligation prohibition .

we use musn't when we think that it is important or essential not to do an action .

we musn't drive fast here.the road sing says that the speed limitis 50 kms per hours   

have to : obligation 

in positive sentences, we often use have to express obligation .in this case, have to is little different form must. 

In Algeria, you have to be 18 before you're allowed to take your driving licence test 

We can use have to to talk about an action that is neccessary.

We have to eat in order to live.Eating is neccessity because there is no other possibility for staying alive .

compare: 

you dont have to/needn't do this exercise .it's optional .Absence /lack  of obligation .

you mustn't cheat in the exam.it's forbidden. Prohibition/ negative obligation .  

Have to, must and needn't

1- We use affirmative and question forms of must' and 'have to' to express obligation.

Example: You must start from here. Do I have to / hæf tə/ start from here?

2 - We use 'must not'/ 'mustn't 'to express prohibition.

Example: You mustn't switch on the computer before quitting the program.

3 - We use 'need not/needn't' and 'do/does not have to to say that there is no obligation to do something.

Example: You needn't/ don't have to send a message. Just phone them.

Note: There is no past form of must. We use 'had to' and 'did not/didn't have to to express obligation and absence of obligation in the past.

Example: I missed the bus yesterday. So I had to / hæt tə/ walk to school.