I could preascertain you could preascertain she could preascertain we could preascertain you could preascertain they could preascertain
V-ing form
I could be preascertaining you could be preascertaining she could be preascertaining we could be preascertaining you could be preascertaining they could be preascertaining
Perfect
I could have preascertained you could have preascertained she could have preascertained we could have preascertained you could have preascertained they could have preascertained
V-ing perfect
I could have been preascertaining you could have been preascertaining she could have been preascertaining we could have been preascertaining you could have been preascertaining they could have been preascertaining
Negation
Simple form
I couldn't preascertain you couldn't preascertain she couldn't preascertain we couldn't preascertain you couldn't preascertain they couldn't preascertain
V-ing form
I couldn't be preascertaining you couldn't be preascertaining she couldn't be preascertaining we couldn't be preascertaining you couldn't be preascertaining they couldn't be preascertaining
Perfect
I couldn't have preascertained you couldn't have preascertained she couldn't have preascertained we couldn't have preascertained you couldn't have preascertained they couldn't have preascertained
V-ing perfect
I couldn't have been preascertaining you couldn't have been preascertaining she couldn't have been preascertaining we couldn't have been preascertaining you couldn't have been preascertaining they couldn't have been preascertaining
Interrogative form
Simple form
could I preascertain? could you preascertain? could she preascertain? could we preascertain? could you preascertain? could they preascertain?
V-ing form
could I be preascertaining? could you be preascertaining? could she be preascertaining? could we be preascertaining? could you be preascertaining? could they be preascertaining?
Perfect
could I have preascertained? could you have preascertained? could she have preascertained? could we have preascertained? could you have preascertained? could they have preascertained?
V-ing perfect
could I have been preascertaining? could you have been preascertaining? could she have been preascertaining? could we have been preascertaining? could you have been preascertaining? could they have been preascertaining?
Interro-negative form
Simple form
couldn't I preascertain? couldn't you preascertain? couldn't she preascertain? couldn't we preascertain? couldn't you preascertain? couldn't they preascertain?
V-ing form
couldn't I be preascertaining? couldn't you be preascertaining? couldn't she be preascertaining? couldn't we be preascertaining? couldn't you be preascertaining? couldn't they be preascertaining?
Perfect
couldn't I have preascertained? couldn't you have preascertained? couldn't she have preascertained? couldn't we have preascertained? couldn't you have preascertained? couldn't they have preascertained?
V-ing perfect
couldn't I have been preascertaining? couldn't you have been preascertaining? couldn't she have been preascertaining? couldn't we have been preascertaining? couldn't you have been preascertaining? couldn't they have been preascertaining?