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 can't knock you can't knock he can't knock we can't knock you can't knock they can't knock	I can't be knocking you can't be knocking he can't be knocking we can't be knocking you can't be knocking they can't be knocking
Perfect	V-ing perfect
I can't have knocked you can't have knocked he can't have knocked we can't have knocked you can't have knocked they can't have knocked	I can't have been knocking you can't have been knocking he can't have been knocking we can't have been knocking you can't have been knocking they can't 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't I knock? can't you knock? can't he knock? can't we knock? can't you knock? can't they knock?	can't I be knocking? can't you be knocking? can't he be knocking? can't we be knocking? can't you be knocking? can't they be knocking?
Perfect	V-ing perfect
can't I have knocked? can't you have knocked? can't he have knocked? can't we have knocked? can't you have knocked? can't they have knocked?	can't I have been knocking? can't you have been knocking? can't he have been knocking? can't we have been knocking? can't you have been knocking? can't they have been knocking?