English verb conjugation
COULD TIGHTEN

Regular verb: tighten - tightened - tightened

Affirmation

Simple form	V-ing form
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
Perfect	V-ing perfect
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
I could not tighten you could not tighten she could not tighten we could not tighten you could not tighten they could not tighten	I could not be tightening you could not be tightening she could not be tightening we could not be tightening you could not be tightening they could not be tightening
Perfect	V-ing perfect
I could not have tightened you could not have tightened she could not have tightened we could not have tightened you could not have tightened they could not have tightened	I could not have been tightening you could not have been tightening she could not have been tightening we could not have been tightening you could not have been tightening they could not have been tightening

Interrogative form

Simple form	V-ing form
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?
Perfect	V-ing perfect
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
could I not tighten? could you not tighten? could she not tighten? could we not tighten? could you not tighten? could they not tighten?	could I not be tightening? could you not be tightening? could she not be tightening? could we not be tightening? could you not be tightening? could they not be tightening?
Perfect	V-ing perfect
could I not have tightened? could you not have tightened? could she not have tightened? could we not have tightened? could you not have tightened? could they not have tightened?	could I not have been tightening? could you not have been tightening? could she not have been tightening? could we not have been tightening? could you not have been tightening? could they not have been tightening?