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 cannot knock you cannot knock she cannot knock we cannot knock you cannot knock they cannot knock	I cannot be knocking you cannot be knocking she 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 she 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 she 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 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 I not knock? can you not knock? can she 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 she 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 she 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 she not have been knocking? can we not have been knocking? can you not have been knocking? can they not have been knocking?