must be Ving or must VR used for saying probability of something

[Sin-Yu Tsai]

When I think someone is studying hard, which sentence below should I say?

You must study hard.

or

You must be studying hard.

I know You must study hard. means You have to study hard., but can it also mean I think you study hard?

Thank you very much.

 

[bhaisahab]

Both are usable for your intended meaning.