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 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
Perfect	V-ing perfect
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
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
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?
Perfect	V-ing perfect
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?