I can ascertain you can ascertain she can ascertain we can ascertain you can ascertain they can ascertain
V-ing form
I can be ascertaining you can be ascertaining she can be ascertaining we can be ascertaining you can be ascertaining they can be ascertaining
Perfect
I can have ascertained you can have ascertained she can have ascertained we can have ascertained you can have ascertained they can have ascertained
V-ing perfect
I can have been ascertaining you can have been ascertaining she can have been ascertaining we can have been ascertaining you can have been ascertaining they can have been ascertaining
Negation
Simple form
I cannot ascertain you cannot ascertain she cannot ascertain we cannot ascertain you cannot ascertain they cannot ascertain
V-ing form
I cannot be ascertaining you cannot be ascertaining she cannot be ascertaining we cannot be ascertaining you cannot be ascertaining they cannot be ascertaining
Perfect
I cannot have ascertained you cannot have ascertained she cannot have ascertained we cannot have ascertained you cannot have ascertained they cannot have ascertained
V-ing perfect
I cannot have been ascertaining you cannot have been ascertaining she cannot have been ascertaining we cannot have been ascertaining you cannot have been ascertaining they cannot have been ascertaining
Interrogative form
Simple form
can I ascertain? can you ascertain? can she ascertain? can we ascertain? can you ascertain? can they ascertain?
V-ing form
can I be ascertaining? can you be ascertaining? can she be ascertaining? can we be ascertaining? can you be ascertaining? can they be ascertaining?
Perfect
can I have ascertained? can you have ascertained? can she have ascertained? can we have ascertained? can you have ascertained? can they have ascertained?
V-ing perfect
can I have been ascertaining? can you have been ascertaining? can she have been ascertaining? can we have been ascertaining? can you have been ascertaining? can they have been ascertaining?
Interro-negative form
Simple form
can I not ascertain? can you not ascertain? can she not ascertain? can we not ascertain? can you not ascertain? can they not ascertain?
V-ing form
can I not be ascertaining? can you not be ascertaining? can she not be ascertaining? can we not be ascertaining? can you not be ascertaining? can they not be ascertaining?
Perfect
can I not have ascertained? can you not have ascertained? can she not have ascertained? can we not have ascertained? can you not have ascertained? can they not have ascertained?
V-ing perfect
can I not have been ascertaining? can you not have been ascertaining? can she not have been ascertaining? can we not have been ascertaining? can you not have been ascertaining? can they not have been ascertaining?