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