could tighten
Regular verb: tighten - tightened- tightened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could tighten
you could tighten
she could tighten
we could tighten
you could tighten
they could tighten 	I could be tightening
you could be tightening
she could be tightening
we could be tightening
you could be tightening
they could be tightening	I could have tightened
you could have tightened
she could have tightened
we could have tightened
you could have tightened
they could have tightened	I could have been tightening
you could have been tightening
she could have been tightening
we could have been tightening
you could have been tightening
they could have been tightening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't tighten
you couldn't tighten
she couldn't tighten
we couldn't tighten
you couldn't tighten
they couldn't tighten 	I couldn't be tightening
you couldn't be tightening
she couldn't be tightening
we couldn't be tightening
you couldn't be tightening
they couldn't be tightening	I couldn't have tightened
you couldn't have tightened
she couldn't have tightened
we couldn't have tightened
you couldn't have tightened
they couldn't have tightened	I couldn't have been tightening
you couldn't have been tightening
she couldn't have been tightening
we couldn't have been tightening
you couldn't have been tightening
they couldn't have been tightening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I tighten?
could you tighten?
could she tighten?
could we tighten?
could you tighten?
could they tighten? 	could I be tightening?
could you be tightening?
could she be tightening?
could we be tightening?
could you be tightening?
could they be tightening? 	could I have tightened?
could you have tightened?
could she have tightened?
could we have tightened?
could you have tightened?
could they have tightened? 	could I have been tightening?
could you have been tightening?
could she have been tightening?
could we have been tightening?
could you have been tightening?
could they have been tightening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I tighten?
couldn't you tighten?
couldn't she tighten?
couldn't we tighten?
couldn't you tighten?
couldn't they tighten? 	couldn't I be tightening?
couldn't you be tightening?
couldn't she be tightening?
couldn't we be tightening?
couldn't you be tightening?
couldn't they be tightening? 	couldn't I have tightened?
couldn't you have tightened?
couldn't she have tightened?
couldn't we have tightened?
couldn't you have tightened?
couldn't they have tightened? 	couldn't I have been tightening?
couldn't you have been tightening?
couldn't she have been tightening?
couldn't we have been tightening?
couldn't you have been tightening?
couldn't they have been tightening?