Could

No one could have done the duty. Or
No one could has done the duty.

Which one is correct?

He could have/has done his duty, if he had gone there. Or
He could do his duty, if he had gone there.

Which one is correct and what is the meaning of both the sentences?

Thank you.

No one could have done the duty. (No one was able to do the duty for some reason not specified here.)
or
No one has done the duty. (No one did the duty, even though they might have been able to do it.)

He could have done his duty if he had gone there. (His duty is in the past and implies he didn’t or the person speaking doesn’t know whether he did or not.)
or
He could do his duty if he went there. (It is in the present, and it is still possible that he could do his duty.)

Thank you, but I also want to know, which one o the above sentences is correct.

No one could have done the duty. or
No one could has done the duty.

What is correct to use with “No one could” “has” or “have”

Thank you.

No one could have done…
No one has done…
Just as I have already stated.

OK, I’ve got this as follows

could/would/may have done ~ a modal plus “have” as the second auxiliary plus the past participle of the main verb is a perfect conditional.

So the perfect conditional always asks for “have” form of the verb to have as the first auxiliary.

Thanks

Thanks a lot both of you :slight_smile: