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