English verb conjugation
COULD LENGTHEN

Regular verb: lengthen - lengthened - lengthened

Affirmation

Simple form	V-ing form
I could lengthen you could lengthen he could lengthen we could lengthen you could lengthen they could lengthen	I could be lengthening you could be lengthening he could be lengthening we could be lengthening you could be lengthening they could be lengthening
Perfect	V-ing perfect
I could have lengthened you could have lengthened he could have lengthened we could have lengthened you could have lengthened they could have lengthened	I could have been lengthening you could have been lengthening he could have been lengthening we could have been lengthening you could have been lengthening they could have been lengthening

Negation

Simple form	V-ing form
I could not lengthen you could not lengthen he could not lengthen we could not lengthen you could not lengthen they could not lengthen	I could not be lengthening you could not be lengthening he could not be lengthening we could not be lengthening you could not be lengthening they could not be lengthening
Perfect	V-ing perfect
I could not have lengthened you could not have lengthened he could not have lengthened we could not have lengthened you could not have lengthened they could not have lengthened	I could not have been lengthening you could not have been lengthening he could not have been lengthening we could not have been lengthening you could not have been lengthening they could not have been lengthening

Interrogative form

Simple form	V-ing form
could I lengthen? could you lengthen? could he lengthen? could we lengthen? could you lengthen? could they lengthen?	could I be lengthening? could you be lengthening? could he be lengthening? could we be lengthening? could you be lengthening? could they be lengthening?
Perfect	V-ing perfect
could I have lengthened? could you have lengthened? could he have lengthened? could we have lengthened? could you have lengthened? could they have lengthened?	could I have been lengthening? could you have been lengthening? could he have been lengthening? could we have been lengthening? could you have been lengthening? could they have been lengthening?

Interro-negative form

Simple form	V-ing form
could I not lengthen? could you not lengthen? could he not lengthen? could we not lengthen? could you not lengthen? could they not lengthen?	could I not be lengthening? could you not be lengthening? could he not be lengthening? could we not be lengthening? could you not be lengthening? could they not be lengthening?
Perfect	V-ing perfect
could I not have lengthened? could you not have lengthened? could he not have lengthened? could we not have lengthened? could you not have lengthened? could they not have lengthened?	could I not have been lengthening? could you not have been lengthening? could he not have been lengthening? could we not have been lengthening? could you not have been lengthening? could they not have been lengthening?