Warning, this verb may not exist. Conjugation is given as example.
Affirmation
Simple form
I could do do you could do do she could do do we could do do you could do do they could do do
V-ing form
I could be do doing you could be do doing she could be do doing we could be do doing you could be do doing they could be do doing
Perfect
I could have do doed you could have do doed she could have do doed we could have do doed you could have do doed they could have do doed
V-ing perfect
I could have been do doing you could have been do doing she could have been do doing we could have been do doing you could have been do doing they could have been do doing
Negation
Simple form
I couldn't do do you couldn't do do she couldn't do do we couldn't do do you couldn't do do they couldn't do do
V-ing form
I couldn't be do doing you couldn't be do doing she couldn't be do doing we couldn't be do doing you couldn't be do doing they couldn't be do doing
Perfect
I couldn't have do doed you couldn't have do doed she couldn't have do doed we couldn't have do doed you couldn't have do doed they couldn't have do doed
V-ing perfect
I couldn't have been do doing you couldn't have been do doing she couldn't have been do doing we couldn't have been do doing you couldn't have been do doing they couldn't have been do doing
Interrogative form
Simple form
could I do do? could you do do? could she do do? could we do do? could you do do? could they do do?
V-ing form
could I be do doing? could you be do doing? could she be do doing? could we be do doing? could you be do doing? could they be do doing?
Perfect
could I have do doed? could you have do doed? could she have do doed? could we have do doed? could you have do doed? could they have do doed?
V-ing perfect
could I have been do doing? could you have been do doing? could she have been do doing? could we have been do doing? could you have been do doing? could they have been do doing?
Interro-negative form
Simple form
couldn't I do do? couldn't you do do? couldn't she do do? couldn't we do do? couldn't you do do? couldn't they do do?
V-ing form
couldn't I be do doing? couldn't you be do doing? couldn't she be do doing? couldn't we be do doing? couldn't you be do doing? couldn't they be do doing?
Perfect
couldn't I have do doed? couldn't you have do doed? couldn't she have do doed? couldn't we have do doed? couldn't you have do doed? couldn't they have do doed?
V-ing perfect
couldn't I have been do doing? couldn't you have been do doing? couldn't she have been do doing? couldn't we have been do doing? couldn't you have been do doing? couldn't they have been do doing?