could intervene
Regular verb: intervene - intervened- intervened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could intervene
you could intervene
he could intervene
we could intervene
you could intervene
they could intervene 	I could be intervening
you could be intervening
he could be intervening
we could be intervening
you could be intervening
they could be intervening	I could have intervened
you could have intervened
he could have intervened
we could have intervened
you could have intervened
they could have intervened	I could have been intervening
you could have been intervening
he could have been intervening
we could have been intervening
you could have been intervening
they could have been intervening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't intervene
you couldn't intervene
he couldn't intervene
we couldn't intervene
you couldn't intervene
they couldn't intervene 	I couldn't be intervening
you couldn't be intervening
he couldn't be intervening
we couldn't be intervening
you couldn't be intervening
they couldn't be intervening	I couldn't have intervened
you couldn't have intervened
he couldn't have intervened
we couldn't have intervened
you couldn't have intervened
they couldn't have intervened	I couldn't have been intervening
you couldn't have been intervening
he couldn't have been intervening
we couldn't have been intervening
you couldn't have been intervening
they couldn't have been intervening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I intervene?
could you intervene?
could he intervene?
could we intervene?
could you intervene?
could they intervene? 	could I be intervening?
could you be intervening?
could he be intervening?
could we be intervening?
could you be intervening?
could they be intervening? 	could I have intervened?
could you have intervened?
could he have intervened?
could we have intervened?
could you have intervened?
could they have intervened? 	could I have been intervening?
could you have been intervening?
could he have been intervening?
could we have been intervening?
could you have been intervening?
could they have been intervening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I intervene?
couldn't you intervene?
couldn't he intervene?
couldn't we intervene?
couldn't you intervene?
couldn't they intervene? 	couldn't I be intervening?
couldn't you be intervening?
couldn't he be intervening?
couldn't we be intervening?
couldn't you be intervening?
couldn't they be intervening? 	couldn't I have intervened?
couldn't you have intervened?
couldn't he have intervened?
couldn't we have intervened?
couldn't you have intervened?
couldn't they have intervened? 	couldn't I have been intervening?
couldn't you have been intervening?
couldn't he have been intervening?
couldn't we have been intervening?
couldn't you have been intervening?
couldn't they have been intervening?