English verb conjugation
CAN KNOCK

Regular verb: knock - knocked - knocked

Affirmation

Simple form	V-ing form
I can knock you can knock she can knock we can knock you can knock they can knock	I can be knocking you can be knocking she 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 she 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 she 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 she 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 she 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 she 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 she 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 she knock? can we knock? can you knock? can they knock?	can I be knocking? can you be knocking? can she 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 she 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 she 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 she 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 she 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 she 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 she have been knocking? can't we have been knocking? can't you have been knocking? can't they have been knocking?