I could let you could let he could let we could let you could let they could let
V-ing form
I could be letting you could be letting he could be letting we could be letting you could be letting they could be letting
Perfect
I could have let you could have let he 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 he could have been letting we could have been letting you could have been letting they could have been letting
Negation
Simple form
I couldn't let you couldn't let he couldn't let we couldn't let you couldn't let they couldn't let
V-ing form
I couldn't be letting you couldn't be letting he couldn't be letting we couldn't be letting you couldn't be letting they couldn't be letting
Perfect
I couldn't have let you couldn't have let he couldn't have let we couldn't have let you couldn't have let they couldn't have let
V-ing perfect
I couldn't have been letting you couldn't have been letting he couldn't have been letting we couldn't have been letting you couldn't have been letting they couldn't have been letting
Interrogative form
Simple form
could I let? could you let? could he let? could we let? could you let? could they let?
V-ing form
could I be letting? could you be letting? could he be letting? could we be letting? could you be letting? could they be letting?
Perfect
could I have let? could you have let? could he 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 he have been letting? could we have been letting? could you have been letting? could they have been letting?
Interro-negative form
Simple form
couldn't I let? couldn't you let? couldn't he let? couldn't we let? couldn't you let? couldn't they let?
V-ing form
couldn't I be letting? couldn't you be letting? couldn't he be letting? couldn't we be letting? couldn't you be letting? couldn't they be letting?
Perfect
couldn't I have let? couldn't you have let? couldn't he have let? couldn't we have let? couldn't you have let? couldn't they have let?
V-ing perfect
couldn't I have been letting? couldn't you have been letting? couldn't he have been letting? couldn't we have been letting? couldn't you have been letting? couldn't they have been letting?