If you don't study hard, you are certain to fail

[keannu]

ex)If you don't study hard, you are certain to fail the exam.

How do you say "certainty" like this? Let me know more common ones.
Can you also say "must"? "you must fail"? No, it doesn't work as it's obligation.

 

[MikeNewYork]

"Must" does not work; "sure" could work.

 

[keannu]

Can you tell me why "must' doesn't work? Do the following sentences work?
1. He is certain/sure to fail.
2. He will surely/certainly fail.

 

[MikeNewYork]

"Must" creates the idea of "obligation" which doesn't exist.

Your other two sentences are fine.

 

[keannu]

Do you think must+action verb always creates obligation, not certainty?

1. He must go/come/call/stay - These are obligations without exception, I guess
2. He must be coming - depending on cotext, it can be either obligation or certainty.
a. He called me he would be coming before coming here, so he must be coming now. - certainty
b. He should turn in to the police for the terrible crime, so right now he must be coming here to the polce station. - obligation..

 

[MikeNewYork]

In my opinion, the word "always" should never be used in a sentence about a modal verb.

 

[keannu]

Please just let me know if the last examples are roughly right, not hundred percent - I need to set up rules, of course, with "some exceptions" label.