must not have been?

[keannu]

Is it possible to say "He must not have been right" for the following of a negative presumption?

ex)He can't have been right.

[5jj]

Is it possible to say "He must not have been right"

It is not impossible, especially if, in speech, we stress 'not'. I don't recommend it.

[Mehrgan]

It is not impossible, especially if, in speech, we stress 'not'. I don't recommend it.

Is it common for the British speakers to say, 'he can't have been right' instead?

[bhaisahab]

Is it common for the British speakers to say, 'he can't have been right' instead?

Yes, it is.

[ostap77]

Yes, it is.

What would be more common to put the negative connotation using "not"or use an adjective that bears the negative meaning itself?

"He could have been wrong." or "He couldn't have been right."

[bhaisahab]

What would be more common to put the negative connotation using "not"or use an adjective that bears the negative meaning itself?

"He could have been wrong." or "He couldn't have been right."

They mean different things. The first means that it's possible that he was wrong and it's possible that he was right. The second means that it's not possible that he was right.