[Grammar] can't be / can't have been...

[deaq]

I've come across a chart that explains Auxiliary. In "can" and "could" part, I don't know if there's any difference in meaning between (a) and (c) or (b) and (d).
Do they mean the same? Or is it just a matter of degree of certainty?

can... Impossibility (negative only)
(a) That can't be true! (Present / Future)
(b) That can't have been true! (Past)
　　
could... Impossibility (negative only)
(c) That couldn't be true! (Present / Future)
(d) That couldn't have been true! (Past)

Thank you in advance.
(I may be late to respond, but I'd appreciate your help.)

 

[sarat_106]

I've come across a chart that explains Auxiliary. In "can" and "could" part, I don't know if there's any difference in meaning between (a) and (c) or (b) and (d).
Do they mean the same? Or is it just a matter of degree of certainty?

can... Impossibility (negative only)
(a) That can't be true! (Present / Future)
(b) That can't have been true! (Past)
　　
could... Impossibility (negative only)
(c) That couldn't be true! (Present / Future)
(d) That couldn't have been true! (Past)

Thank you in advance.
(I may be late to respond, but I'd appreciate your help.)

Yes, there is, which can be termed as a small grammatical nuances.

a) That can't be true! (Present / Future) The report says, people in Beijing buy about 1,000 cars a day (a fact related to recent present progress)
(b) That can't have been true! (Past) of president Bush.( something that refers to a time considered very recent in relation to the moment of utterance.
　　
could... Impossibility (negative only)
(c) That couldn't be true! (Present / Future), If you check Obama's last trip overseas, his wife left just after their visit to France (a fact related to distant present)
(d) That couldn't have been true! (Past) of president Kenedy(a fact related to distant past or the past beyond individual memory)

 

[deaq]

I see... I think I'm beginning to understand the difference.

Thank you for your time and help!!