I could fork you could fork she could fork we could fork you could fork they could fork
V-ing form
I could be forking you could be forking she could be forking we could be forking you could be forking they could be forking
Perfect
I could have forked you could have forked she 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 she 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 she 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 she 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 she 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 she 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 she fork? could we fork? could you fork? could they fork?
V-ing form
could I be forking? could you be forking? could she be forking? could we be forking? could you be forking? could they be forking?
Perfect
could I have forked? could you have forked? could she 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 she 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 she 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 she 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 she 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 she have been forking? couldn't we have been forking? couldn't you have been forking? couldn't they have been forking?