I can knock you can knock he can knock we can knock you can knock they can knock
Forma con V-ing
I can be knocking you can be knocking he can be knocking we can be knocking you can be knocking they can be knocking
Perfecto
I can have knocked you can have knocked he can have knocked we can have knocked you can have knocked they can have knocked
Perfecto con V-ing
I can have been knocking you can have been knocking he can have been knocking we can have been knocking you can have been knocking they can have been knocking
Negación
Forma simple
I can't knock you can't knock he can't knock we can't knock you can't knock they can't knock
Forma con V-ing
I can't be knocking you can't be knocking he can't be knocking we can't be knocking you can't be knocking they can't be knocking
Perfecto
I can't have knocked you can't have knocked he can't have knocked we can't have knocked you can't have knocked they can't have knocked
Perfecto con V-ing
I can't have been knocking you can't have been knocking he can't have been knocking we can't have been knocking you can't have been knocking they can't have been knocking
Forma interrogativa
Forma simple
can I knock? can you knock? can he knock? can we knock? can you knock? can they knock?
Forma con V-ing
can I be knocking? can you be knocking? can he be knocking? can we be knocking? can you be knocking? can they be knocking?
Perfecto
can I have knocked? can you have knocked? can he have knocked? can we have knocked? can you have knocked? can they have knocked?
Perfecto con V-ing
can I have been knocking? can you have been knocking? can he have been knocking? can we have been knocking? can you have been knocking? can they have been knocking?
Forma interro-negativa
Forma simple
can't I knock? can't you knock? can't he knock? can't we knock? can't you knock? can't they knock?
Forma con V-ing
can't I be knocking? can't you be knocking? can't he be knocking? can't we be knocking? can't you be knocking? can't they be knocking?
Perfecto
can't I have knocked? can't you have knocked? can't he have knocked? can't we have knocked? can't you have knocked? can't they have knocked?
Perfecto con V-ing
can't I have been knocking? can't you have been knocking? can't he have been knocking? can't we have been knocking? can't you have been knocking? can't they have been knocking?