Grammar - Modals - Express Certainty

[123Amigo]

Good evening,

I am currently working on my grammar skills, especially the modals. I finished an exercise a couple of minutes ago, but now I am confused.

The grammar within the same book told me that the negative form of can or could is used to express certainty.
They also say that could is the past form of can.

The example is:

It's unlikely she was enjoying herself very much.

The task is to form a the rest of a given modal sentence:

She can't have been enjoying herself very much.
This is the answer given in the correction.

Why do they use can't? I would suggest to use couldn't as we are dealing with a past tense. The tense in the example is past progressive not present progressive?

I hope you can give me a more useful explanation.

Kind regards and thank you very much!

[bhaisahab]

Good evening,

I am currently working on my grammar skills, especially the modals. I finished an exercise a couple of minutes ago, but now I am confused.

The grammar within the same book told me that the negative form of can or could is used to express certainty.
They also say that could is the past form of can.

The example is:

It's unlikely she was enjoying herself very much.

The task is to form a the rest of a given modal sentence:

She can't have been enjoying herself very much.
This is the answer given in the correction.

Why do they use can't? I would suggest to use couldn't as we are dealing with a past tense. The tense in the example is past progressive not present progressive?

I hope you can give me a more useful explanation.

Kind regards and thank you very much!

"She can't have been enjoying herself very much." This is present perfect progressive.

[5jj]

"She can't have been enjoying herself very much." This is present perfect progressive.

I have to disagree with you there, bhai.
For me, the present perfect progressive would be: She hasn't been enjoying herself. If I had to label She can't have been enjoying herself , I'd go for 'modal perfect progressive'.

Ignoring labelling, amigo, does this make sense? -

She must be working: - It is logically certain (now) that she is working (now).
She can't be working: - It is logically certain (now) that she isn't working (now).

She must have been working: - It is logically certain (now) that she was working (in the past) or has been working (from the past up till now).
She can't have been working: - It is logically certain (now) that she wasn't working (in the past) or hasn't been working (from the past up till now.

When I saw her yesterday she was fresh as a daisy. She couldn't have been working: - It was logically certain (in the past) that she hadn't been working (at a previous past time, or from a previous past time up till the past time spoken of).

[Khosro]

Just as an end note for 123Amigo:
"She can't" stands for "It is unlikely", and they are both in present tense.