I could ko you could ko he could ko we could ko you could ko they could ko
V-ing form
I could be koing you could be koing he could be koing we could be koing you could be koing they could be koing
Perfect
I could have koed you could have koed he 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 he 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 he 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 he 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 he 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 he 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 he ko? could we ko? could you ko? could they ko?
V-ing form
could I be koing? could you be koing? could he be koing? could we be koing? could you be koing? could they be koing?
Perfect
could I have koed? could you have koed? could he 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 he 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 he 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 he 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 he 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 he have been koing? couldn't we have been koing? couldn't you have been koing? couldn't they have been koing?