could thread
Regular verb: thread - threaded- threaded

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