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