'can' vs 'could'

[Truebytes]

hi,

can somebody help the uses of following clauses

I can be the
I can't be the
I can't have
I can't have been
I couldn't have

I always confuse about this....

[Swapnil.Kale]

Can is used to express the ability to do something.

e.g
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I doubt on "I can't have been..". I've never came across such sentence.

Regards,
Swapnil.

[Haihao]

e.g. 'I can't have been that careless', which would suggest: it's reasonable to think that I was not that careless (but actually I was careless with something at sometime).