could weaken
Regular verb: weaken - weakened- weakened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could weaken
you could weaken
he could weaken
we could weaken
you could weaken
they could weaken 	I could be weakening
you could be weakening
he could be weakening
we could be weakening
you could be weakening
they could be weakening	I could have weakened
you could have weakened
he could have weakened
we could have weakened
you could have weakened
they could have weakened	I could have been weakening
you could have been weakening
he could have been weakening
we could have been weakening
you could have been weakening
they could have been weakening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't weaken
you couldn't weaken
he couldn't weaken
we couldn't weaken
you couldn't weaken
they couldn't weaken 	I couldn't be weakening
you couldn't be weakening
he couldn't be weakening
we couldn't be weakening
you couldn't be weakening
they couldn't be weakening	I couldn't have weakened
you couldn't have weakened
he couldn't have weakened
we couldn't have weakened
you couldn't have weakened
they couldn't have weakened	I couldn't have been weakening
you couldn't have been weakening
he couldn't have been weakening
we couldn't have been weakening
you couldn't have been weakening
they couldn't have been weakening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I weaken?
could you weaken?
could he weaken?
could we weaken?
could you weaken?
could they weaken? 	could I be weakening?
could you be weakening?
could he be weakening?
could we be weakening?
could you be weakening?
could they be weakening? 	could I have weakened?
could you have weakened?
could he have weakened?
could we have weakened?
could you have weakened?
could they have weakened? 	could I have been weakening?
could you have been weakening?
could he have been weakening?
could we have been weakening?
could you have been weakening?
could they have been weakening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I weaken?
couldn't you weaken?
couldn't he weaken?
couldn't we weaken?
couldn't you weaken?
couldn't they weaken? 	couldn't I be weakening?
couldn't you be weakening?
couldn't he be weakening?
couldn't we be weakening?
couldn't you be weakening?
couldn't they be weakening? 	couldn't I have weakened?
couldn't you have weakened?
couldn't he have weakened?
couldn't we have weakened?
couldn't you have weakened?
couldn't they have weakened? 	couldn't I have been weakening?
couldn't you have been weakening?
couldn't he have been weakening?
couldn't we have been weakening?
couldn't you have been weakening?
couldn't they have been weakening?