The most common use: the generic bond

This is the job that you normally know the most, so I surely won't be surprised if I tell you that having to and having to usually translate into obligation, of whatever nature. To say that something is necessary and obligatory, we use modal must, which is like every modal ALWAYS FOLLOWED by a verbal base!

President Trump must keep his word and testify before Congress. // President Trump must bear true to his words and testify before Congress.
The other possibility is to use the have to + BV construction, especially to translate the impersonal construction you need + proposition.

You need to do your homework. // You have to do your homework.
Now the question is when to use must and when to use have to. Know that in the present, we have the choice between the two. However, when it is the speaker who exposes the obligation, must be privileged. Otherwise, it's have to.

All citizens must obey the curfew or face a fine. // All citizens have to abide by the curfew or financial penalties may ensue.
You must go there. // You must go.
In addition, we must use have to when must cannot be used, i.e. after a modal (will or should for example), after to, to refer to the past tense (had to), the present perfect and the past perfect.

He will have to do what is expected of him. // He will have to do what is expected of him.
It’s unbearable to have to scold him for the umpteenth time. // It’s unbearable to have to blame him for the umpteenth time.
We had to visit his mother on Sunday. // We had to visit her mother on Sunday.
We had to take him to the hospital. // We have had to taker her to the hospital.

The board

To translate should and should expressing advice ("you should do this" or "you should do this"), you can either use the modal should, or the construction ought to + BV which has a moral connotation.

Easy as pie, just remember these two, that will be more than enough for you.

You shouldn't be eating that much. // You shouldn’t eat that much.

The probability

This case applies to the translation of the verb should in clauses such as "he must have done this", "it must have been eight o'clock when ..." or even "he must be far by now. ".

Note first of all that to express a high probability in the present tense, we most often use must followed by the BV, and in the past tense, the construction must + have + past participle. Once again, especially remember this canonical case, it will serve you all the time!

He had to go out. // He must have gone out.
He must be forty years old. // He must be forty. (N.B .: to reinforce the idea of ​​probability on this turn, you can add at the end, he must be forty, if he is a day. It's a little idiomatic expression that works very well, especially in translation!)
To express the high probability in the future, you can use the will modal instead of the must modal.

He should definitely take over the business. // He will be appointed as the new CEO of the company.

Translate need for necessity (I need this, I need that)

Again it's very simple, this time you have to use a semi-modal, namely need.

I need 10 euros. // I need 10 euros.

Here, I have given you the broad outline, with these examples you will know how to deal with all the simple cases where the slightest mistake is crippling! Just remember that for each case, you have to associate the right modal!