could extinguish
Regular verb: extinguish - extinguished- extinguished

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could extinguish
you could extinguish
he could extinguish
we could extinguish
you could extinguish
they could extinguish 	I could be extinguishing
you could be extinguishing
he could be extinguishing
we could be extinguishing
you could be extinguishing
they could be extinguishing	I could have extinguished
you could have extinguished
he could have extinguished
we could have extinguished
you could have extinguished
they could have extinguished	I could have been extinguishing
you could have been extinguishing
he could have been extinguishing
we could have been extinguishing
you could have been extinguishing
they could have been extinguishing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not extinguish
you could not extinguish
he could not extinguish
we could not extinguish
you could not extinguish
they could not extinguish 	I could not be extinguishing
you could not be extinguishing
he could not be extinguishing
we could not be extinguishing
you could not be extinguishing
they could not be extinguishing	I could not have extinguished
you could not have extinguished
he could not have extinguished
we could not have extinguished
you could not have extinguished
they could not have extinguished	I could not have been extinguishing
you could not have been extinguishing
he could not have been extinguishing
we could not have been extinguishing
you could not have been extinguishing
they could not have been extinguishing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I extinguish?
could you extinguish?
could he extinguish?
could we extinguish?
could you extinguish?
could they extinguish? 	could I be extinguishing?
could you be extinguishing?
could he be extinguishing?
could we be extinguishing?
could you be extinguishing?
could they be extinguishing? 	could I have extinguished?
could you have extinguished?
could he have extinguished?
could we have extinguished?
could you have extinguished?
could they have extinguished? 	could I have been extinguishing?
could you have been extinguishing?
could he have been extinguishing?
could we have been extinguishing?
could you have been extinguishing?
could they have been extinguishing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not extinguish?
could you not extinguish?
could he not extinguish?
could we not extinguish?
could you not extinguish?
could they not extinguish? 	could I not be extinguishing?
could you not be extinguishing?
could he not be extinguishing?
could we not be extinguishing?
could you not be extinguishing?
could they not be extinguishing? 	could I not have extinguished?
could you not have extinguished?
could he not have extinguished?
could we not have extinguished?
could you not have extinguished?
could they not have extinguished? 	could I not have been extinguishing?
could you not have been extinguishing?
could he not have been extinguishing?
could we not have been extinguishing?
could you not have been extinguishing?
could they not have been extinguishing?