I could thread you could thread she could thread we could thread you could thread they could thread
V-ing form
I could be threading you could be threading she could be threading we could be threading you could be threading they could be threading
Perfect
I could have threaded you could have threaded she could have threaded we could have threaded you could have threaded they could have threaded
V-ing perfect
I could have been threading you could have been threading she could have been threading we could have been threading you could have been threading they could have been threading
Negation
Simple form
I couldn't thread you couldn't thread she couldn't thread we couldn't thread you couldn't thread they couldn't thread
V-ing form
I couldn't be threading you couldn't be threading she couldn't be threading we couldn't be threading you couldn't be threading they couldn't be threading
Perfect
I couldn't have threaded you couldn't have threaded she couldn't have threaded we couldn't have threaded you couldn't have threaded they couldn't have threaded
V-ing perfect
I couldn't have been threading you couldn't have been threading she couldn't have been threading we couldn't have been threading you couldn't have been threading they couldn't have been threading
Interrogative form
Simple form
could I thread? could you thread? could she thread? could we thread? could you thread? could they thread?
V-ing form
could I be threading? could you be threading? could she be threading? could we be threading? could you be threading? could they be threading?
Perfect
could I have threaded? could you have threaded? could she have threaded? could we have threaded? could you have threaded? could they have threaded?
V-ing perfect
could I have been threading? could you have been threading? could she have been threading? could we have been threading? could you have been threading? could they have been threading?
Interro-negative form
Simple form
couldn't I thread? couldn't you thread? couldn't she thread? couldn't we thread? couldn't you thread? couldn't they thread?
V-ing form
couldn't I be threading? couldn't you be threading? couldn't she be threading? couldn't we be threading? couldn't you be threading? couldn't they be threading?
Perfect
couldn't I have threaded? couldn't you have threaded? couldn't she have threaded? couldn't we have threaded? couldn't you have threaded? couldn't they have threaded?
V-ing perfect
couldn't I have been threading? couldn't you have been threading? couldn't she have been threading? couldn't we have been threading? couldn't you have been threading? couldn't they have been threading?