"have been unable" vs "was unable"

[subhajit123]

Hi there, I have a question related to usage of have been unable and was unable. I have provided contexts reagrding this below.

• Tom is a very brilliant student. John is/was a good student too but he has achieved what John has been/was unable to do.

I think I should use "present perfect" in the context if john is still a student. And if he is not a student any more or dead, I think I should use past tense. I want your opinions.


One more question, Could you please tell me which tense I should choose in the following context?

• I am proud of my son. He has earned so much money and lots of respect. He has achieved something that I was/have been unable to do in the last 20 years.

 

[GoesStation]

For number two, in the last twenty years makes the past simple inappropriate.

Always spell out small numbers.

 

[subhajit123]

Thank you. So in the first sentence, Are both "present perfect" and "past tense" interchangeable?

 

[subhajit123]

Your first sentence is 'Tom is a [STRIKE]very[/STRIKE] brilliant student'. The tense/aspect you use for the verb I have underlined depends on how you wish to present the period of time in which he was/hasbeen/is a student.

Thank you. But my question is if I say "Tom is a brilliant student but he is lazy. John is not as good student as Tom but he is hardworking. Therefore, John has achieved what Tom was/has been unable to do.", does that sound natural and grammatical?

Note that John is still a student.

 

[GoesStation]

It's hard to answer questions like yours; the text is illogical because a brilliant student naturally achieves more than another student who is merely hardworking. Let's revise your quote as follows:

Tom is brilliant but lazy. John is not as smart as Tom but he is hardworking. Therefore, John has achieved what Tom was/has been unable to do.

With my revision, the present perfect has been is more natural.