I could tough you could tough he could tough we could tough you could tough they could tough
V-ing form
I could be toughing you could be toughing he could be toughing we could be toughing you could be toughing they could be toughing
Perfect
I could have toughed you could have toughed he could have toughed we could have toughed you could have toughed they could have toughed
V-ing perfect
I could have been toughing you could have been toughing he could have been toughing we could have been toughing you could have been toughing they could have been toughing
Negation
Simple form
I could not tough you could not tough he could not tough we could not tough you could not tough they could not tough
V-ing form
I could not be toughing you could not be toughing he could not be toughing we could not be toughing you could not be toughing they could not be toughing
Perfect
I could not have toughed you could not have toughed he could not have toughed we could not have toughed you could not have toughed they could not have toughed
V-ing perfect
I could not have been toughing you could not have been toughing he could not have been toughing we could not have been toughing you could not have been toughing they could not have been toughing
Interrogative form
Simple form
could I tough? could you tough? could he tough? could we tough? could you tough? could they tough?
V-ing form
could I be toughing? could you be toughing? could he be toughing? could we be toughing? could you be toughing? could they be toughing?
Perfect
could I have toughed? could you have toughed? could he have toughed? could we have toughed? could you have toughed? could they have toughed?
V-ing perfect
could I have been toughing? could you have been toughing? could he have been toughing? could we have been toughing? could you have been toughing? could they have been toughing?
Interro-negative form
Simple form
could I not tough? could you not tough? could he not tough? could we not tough? could you not tough? could they not tough?
V-ing form
could I not be toughing? could you not be toughing? could he not be toughing? could we not be toughing? could you not be toughing? could they not be toughing?
Perfect
could I not have toughed? could you not have toughed? could he not have toughed? could we not have toughed? could you not have toughed? could they not have toughed?
V-ing perfect
could I not have been toughing? could you not have been toughing? could he not have been toughing? could we not have been toughing? could you not have been toughing? could they not have been toughing?