He has already studied history for two hours.

[sitifan]

He has already studied history for two hours.

Is the above sentence acceptable?

[Rover_KE]

It could be - depending on the context.

How do you want to use this sentence?

Rover

[shroob]

He has already studied history for two hours.

Is the above sentence acceptable?

Yes.

A: Can Mark come out to play now Mrs. Jones?
Mrs. Jones: No, he has homework to do.
A: He's already studied history for two hours.
Mrs. Jones: Sorry.

[5jj]

Yes.

A: Can Mark come out to play now Mrs. Jones?
Mrs. Jones: No, he has homework to do.
A: He's already studied history for two hours.
Mrs. Jones: Sorry.

In this particular example, "He has already been studying (history) for two hours" appears more natural to me.

I cannot think of a context for 'study', 'already, 'history' in which the non-progressive form is natural for such a short period as two hours. That is not to say that it's not possible.

[Rover_KE]

In this particular example, "He has already been studying (history) for two hours" appears more natural to me.

I cannot think of a context for 'study', 'already, 'history' in which the non-progressive form is natural for such a short period as two hours. That is not to say that it's not possible.

I agree with 5.

In my opinion the OP should be giving us the context in which he wants to use this unusual construction rather than expecting us to devise a situation in which he might possibly use it.

Rover