Affirmative (+) form
Can comes first in the verb phrase (after the subject and before another verb):
We [verb phrase]can take the train to Birmingham.
Can is never used with another modal verb:
He can hear the music from his room sometimes.
Not:
He can might hear the music… orHe might can might hear the music…
Negative (−) form
The negative form of can is can’t. We don’t use don’t/doesn’t/didn’t with can:
I can’t believe you said that!
Not:
I don’t can believe you said that!
We can use the full form cannot (one word) in formal contexts or when we want to emphasise something:
I cannot understand why she behaves like that.
Question (?) form
The subject and can change position to form questions. We don’t use do/does/did:
Can this really be true?
Not:
Does this can really be true?
Can’t you ask for another day off work?
We use can and can’t in question tags:
You can’t take photos inside the museum, can you?
Abby can speak Japanese, can’t she?