English verb conjugation
CAN KNOCK

Regular verb: knock - knocked - knocked

Affirmation

Simple form	V-ing form
I can knock you can knock he can knock we can knock you can knock they can knock	I can be knocking you can be knocking he can be knocking we can be knocking you can be knocking they can be knocking
Perfect	V-ing perfect
I can have knocked you can have knocked he can have knocked we can have knocked you can have knocked they can have knocked	I can have been knocking you can have been knocking he can have been knocking we can have been knocking you can have been knocking they can have been knocking

Negation

Simple form	V-ing form
I cannot knock you cannot knock he cannot knock we cannot knock you cannot knock they cannot knock	I cannot be knocking you cannot be knocking he cannot be knocking we cannot be knocking you cannot be knocking they cannot be knocking
Perfect	V-ing perfect
I cannot have knocked you cannot have knocked he cannot have knocked we cannot have knocked you cannot have knocked they cannot have knocked	I cannot have been knocking you cannot have been knocking he cannot have been knocking we cannot have been knocking you cannot have been knocking they cannot have been knocking

Interrogative form

Simple form	V-ing form
can I knock? can you knock? can he knock? can we knock? can you knock? can they knock?	can I be knocking? can you be knocking? can he be knocking? can we be knocking? can you be knocking? can they be knocking?
Perfect	V-ing perfect
can I have knocked? can you have knocked? can he have knocked? can we have knocked? can you have knocked? can they have knocked?	can I have been knocking? can you have been knocking? can he have been knocking? can we have been knocking? can you have been knocking? can they have been knocking?

Interro-negative form

Simple form	V-ing form
can I not knock? can you not knock? can he not knock? can we not knock? can you not knock? can they not knock?	can I not be knocking? can you not be knocking? can he not be knocking? can we not be knocking? can you not be knocking? can they not be knocking?
Perfect	V-ing perfect
can I not have knocked? can you not have knocked? can he not have knocked? can we not have knocked? can you not have knocked? can they not have knocked?	can I not have been knocking? can you not have been knocking? can he not have been knocking? can we not have been knocking? can you not have been knocking? can they not have been knocking?