I could let you could let she could let we could let you could let they could let
V-ing form
I could be letting you could be letting she could be letting we could be letting you could be letting they could be letting
Perfect
I could have let you could have let she could have let we could have let you could have let they could have let
V-ing perfect
I could have been letting you could have been letting she could have been letting we could have been letting you could have been letting they could have been letting
Negation
Simple form
I could not let you could not let she could not let we could not let you could not let they could not let
V-ing form
I could not be letting you could not be letting she could not be letting we could not be letting you could not be letting they could not be letting
Perfect
I could not have let you could not have let she could not have let we could not have let you could not have let they could not have let
V-ing perfect
I could not have been letting you could not have been letting she could not have been letting we could not have been letting you could not have been letting they could not have been letting
Interrogative form
Simple form
could I let? could you let? could she let? could we let? could you let? could they let?
V-ing form
could I be letting? could you be letting? could she be letting? could we be letting? could you be letting? could they be letting?
Perfect
could I have let? could you have let? could she have let? could we have let? could you have let? could they have let?
V-ing perfect
could I have been letting? could you have been letting? could she have been letting? could we have been letting? could you have been letting? could they have been letting?
Interro-negative form
Simple form
could I not let? could you not let? could she not let? could we not let? could you not let? could they not let?
V-ing form
could I not be letting? could you not be letting? could she not be letting? could we not be letting? could you not be letting? could they not be letting?
Perfect
could I not have let? could you not have let? could she not have let? could we not have let? could you not have let? could they not have let?
V-ing perfect
could I not have been letting? could you not have been letting? could she not have been letting? could we not have been letting? could you not have been letting? could they not have been letting?