I could fork you could fork he could fork we could fork you could fork they could fork
V-ing form
I could be forking you could be forking he could be forking we could be forking you could be forking they could be forking
Perfect
I could have forked you could have forked he could have forked we could have forked you could have forked they could have forked
V-ing perfect
I could have been forking you could have been forking he could have been forking we could have been forking you could have been forking they could have been forking
Negation
Simple form
I couldn't fork you couldn't fork he couldn't fork we couldn't fork you couldn't fork they couldn't fork
V-ing form
I couldn't be forking you couldn't be forking he couldn't be forking we couldn't be forking you couldn't be forking they couldn't be forking
Perfect
I couldn't have forked you couldn't have forked he couldn't have forked we couldn't have forked you couldn't have forked they couldn't have forked
V-ing perfect
I couldn't have been forking you couldn't have been forking he couldn't have been forking we couldn't have been forking you couldn't have been forking they couldn't have been forking
Interrogative form
Simple form
could I fork? could you fork? could he fork? could we fork? could you fork? could they fork?
V-ing form
could I be forking? could you be forking? could he be forking? could we be forking? could you be forking? could they be forking?
Perfect
could I have forked? could you have forked? could he have forked? could we have forked? could you have forked? could they have forked?
V-ing perfect
could I have been forking? could you have been forking? could he have been forking? could we have been forking? could you have been forking? could they have been forking?
Interro-negative form
Simple form
couldn't I fork? couldn't you fork? couldn't he fork? couldn't we fork? couldn't you fork? couldn't they fork?
V-ing form
couldn't I be forking? couldn't you be forking? couldn't he be forking? couldn't we be forking? couldn't you be forking? couldn't they be forking?
Perfect
couldn't I have forked? couldn't you have forked? couldn't he have forked? couldn't we have forked? couldn't you have forked? couldn't they have forked?
V-ing perfect
couldn't I have been forking? couldn't you have been forking? couldn't he have been forking? couldn't we have been forking? couldn't you have been forking? couldn't they have been forking?