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