could lighten
Regular verb: lighten - lightened- lightened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could lighten
you could lighten
she could lighten
we could lighten
you could lighten
they could lighten 	I could be lightening
you could be lightening
she could be lightening
we could be lightening
you could be lightening
they could be lightening	I could have lightened
you could have lightened
she could have lightened
we could have lightened
you could have lightened
they could have lightened	I could have been lightening
you could have been lightening
she could have been lightening
we could have been lightening
you could have been lightening
they could have been lightening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not lighten
you could not lighten
she could not lighten
we could not lighten
you could not lighten
they could not lighten 	I could not be lightening
you could not be lightening
she could not be lightening
we could not be lightening
you could not be lightening
they could not be lightening	I could not have lightened
you could not have lightened
she could not have lightened
we could not have lightened
you could not have lightened
they could not have lightened	I could not have been lightening
you could not have been lightening
she could not have been lightening
we could not have been lightening
you could not have been lightening
they could not have been lightening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I lighten?
could you lighten?
could she lighten?
could we lighten?
could you lighten?
could they lighten? 	could I be lightening?
could you be lightening?
could she be lightening?
could we be lightening?
could you be lightening?
could they be lightening? 	could I have lightened?
could you have lightened?
could she have lightened?
could we have lightened?
could you have lightened?
could they have lightened? 	could I have been lightening?
could you have been lightening?
could she have been lightening?
could we have been lightening?
could you have been lightening?
could they have been lightening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not lighten?
could you not lighten?
could she not lighten?
could we not lighten?
could you not lighten?
could they not lighten? 	could I not be lightening?
could you not be lightening?
could she not be lightening?
could we not be lightening?
could you not be lightening?
could they not be lightening? 	could I not have lightened?
could you not have lightened?
could she not have lightened?
could we not have lightened?
could you not have lightened?
could they not have lightened? 	could I not have been lightening?
could you not have been lightening?
could she not have been lightening?
could we not have been lightening?
could you not have been lightening?
could they not have been lightening?