could ascertain
Regular verb: ascertain - ascertained- ascertained

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could ascertain
you could ascertain
he could ascertain
we could ascertain
you could ascertain
they could ascertain 	I could be ascertaining
you could be ascertaining
he could be ascertaining
we could be ascertaining
you could be ascertaining
they could be ascertaining	I could have ascertained
you could have ascertained
he could have ascertained
we could have ascertained
you could have ascertained
they could have ascertained	I could have been ascertaining
you could have been ascertaining
he could have been ascertaining
we could have been ascertaining
you could have been ascertaining
they could have been ascertaining	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't ascertain
you couldn't ascertain
he couldn't ascertain
we couldn't ascertain
you couldn't ascertain
they couldn't ascertain 	I couldn't be ascertaining
you couldn't be ascertaining
he couldn't be ascertaining
we couldn't be ascertaining
you couldn't be ascertaining
they couldn't be ascertaining	I couldn't have ascertained
you couldn't have ascertained
he couldn't have ascertained
we couldn't have ascertained
you couldn't have ascertained
they couldn't have ascertained	I couldn't have been ascertaining
you couldn't have been ascertaining
he couldn't have been ascertaining
we couldn't have been ascertaining
you couldn't have been ascertaining
they couldn't have been ascertaining	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I ascertain?
could you ascertain?
could he ascertain?
could we ascertain?
could you ascertain?
could they ascertain? 	could I be ascertaining?
could you be ascertaining?
could he be ascertaining?
could we be ascertaining?
could you be ascertaining?
could they be ascertaining? 	could I have ascertained?
could you have ascertained?
could he have ascertained?
could we have ascertained?
could you have ascertained?
could they have ascertained? 	could I have been ascertaining?
could you have been ascertaining?
could he have been ascertaining?
could we have been ascertaining?
could you have been ascertaining?
could they have been ascertaining? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I ascertain?
couldn't you ascertain?
couldn't he ascertain?
couldn't we ascertain?
couldn't you ascertain?
couldn't they ascertain? 	couldn't I be ascertaining?
couldn't you be ascertaining?
couldn't he be ascertaining?
couldn't we be ascertaining?
couldn't you be ascertaining?
couldn't they be ascertaining? 	couldn't I have ascertained?
couldn't you have ascertained?
couldn't he have ascertained?
couldn't we have ascertained?
couldn't you have ascertained?
couldn't they have ascertained? 	couldn't I have been ascertaining?
couldn't you have been ascertaining?
couldn't he have been ascertaining?
couldn't we have been ascertaining?
couldn't you have been ascertaining?
couldn't they have been ascertaining?