I could thread you could thread he could thread we could thread you could thread they could thread
V-ing form
I could be threading you could be threading he could be threading we could be threading you could be threading they could be threading
Perfect
I could have threaded you could have threaded he 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 he 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 he 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 he 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 he 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 he 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 he thread? could we thread? could you thread? could they thread?
V-ing form
could I be threading? could you be threading? could he be threading? could we be threading? could you be threading? could they be threading?
Perfect
could I have threaded? could you have threaded? could he 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 he 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 he 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 he 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 he 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 he have been threading? couldn't we have been threading? couldn't you have been threading? couldn't they have been threading?