English verb conjugation
COULD KNOCK

Regular verb: knock - knocked - knocked

Affirmation

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

Negation

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

Interrogative form

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

Interro-negative form

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