I could scratch you could scratch he could scratch we could scratch you could scratch they could scratch
V-ing form
I could be scratching you could be scratching he could be scratching we could be scratching you could be scratching they could be scratching
Perfect
I could have scratched you could have scratched he could have scratched we could have scratched you could have scratched they could have scratched
V-ing perfect
I could have been scratching you could have been scratching he could have been scratching we could have been scratching you could have been scratching they could have been scratching
Negation
Simple form
I could not scratch you could not scratch he could not scratch we could not scratch you could not scratch they could not scratch
V-ing form
I could not be scratching you could not be scratching he could not be scratching we could not be scratching you could not be scratching they could not be scratching
Perfect
I could not have scratched you could not have scratched he could not have scratched we could not have scratched you could not have scratched they could not have scratched
V-ing perfect
I could not have been scratching you could not have been scratching he could not have been scratching we could not have been scratching you could not have been scratching they could not have been scratching
Interrogative form
Simple form
could I scratch? could you scratch? could he scratch? could we scratch? could you scratch? could they scratch?
V-ing form
could I be scratching? could you be scratching? could he be scratching? could we be scratching? could you be scratching? could they be scratching?
Perfect
could I have scratched? could you have scratched? could he have scratched? could we have scratched? could you have scratched? could they have scratched?
V-ing perfect
could I have been scratching? could you have been scratching? could he have been scratching? could we have been scratching? could you have been scratching? could they have been scratching?
Interro-negative form
Simple form
could I not scratch? could you not scratch? could he not scratch? could we not scratch? could you not scratch? could they not scratch?
V-ing form
could I not be scratching? could you not be scratching? could he not be scratching? could we not be scratching? could you not be scratching? could they not be scratching?
Perfect
could I not have scratched? could you not have scratched? could he not have scratched? could we not have scratched? could you not have scratched? could they not have scratched?
V-ing perfect
could I not have been scratching? could you not have been scratching? could he not have been scratching? could we not have been scratching? could you not have been scratching? could they not have been scratching?