could have been vs. could have become

[preissmurphy]

I have a student that wants me to explain the difference between:

could have been -and- could have become

The example he gave me:

" He could have been someone great, if he had only worked harder at his goals"
"He could have become someone great, if he had only worked harder at his goals"

Is there a difference? How would I explain this to the student? Is there a rule?

Thanks

[cerealkillah]

In my opinion there is no significant difference, apart from the one between "be" and "become". However, in this case (unreal past, or hypothetical event in the past) it doesn't matter if we refer to a certain point in time (become) or some broader time (be). What matters is that "he isn't anyone great today".

[Susan]

I agree with cerealkillah