I can biff you can biff he can biff we can biff you can biff they can biff
V-ing form
I can be biffing you can be biffing he can be biffing we can be biffing you can be biffing they can be biffing
Perfect
I can have biffed you can have biffed he can have biffed we can have biffed you can have biffed they can have biffed
V-ing perfect
I can have been biffing you can have been biffing he can have been biffing we can have been biffing you can have been biffing they can have been biffing
Negation
Simple form
I cannot biff you cannot biff he cannot biff we cannot biff you cannot biff they cannot biff
V-ing form
I cannot be biffing you cannot be biffing he cannot be biffing we cannot be biffing you cannot be biffing they cannot be biffing
Perfect
I cannot have biffed you cannot have biffed he cannot have biffed we cannot have biffed you cannot have biffed they cannot have biffed
V-ing perfect
I cannot have been biffing you cannot have been biffing he cannot have been biffing we cannot have been biffing you cannot have been biffing they cannot have been biffing
Interrogative form
Simple form
can I biff? can you biff? can he biff? can we biff? can you biff? can they biff?
V-ing form
can I be biffing? can you be biffing? can he be biffing? can we be biffing? can you be biffing? can they be biffing?
Perfect
can I have biffed? can you have biffed? can he have biffed? can we have biffed? can you have biffed? can they have biffed?
V-ing perfect
can I have been biffing? can you have been biffing? can he have been biffing? can we have been biffing? can you have been biffing? can they have been biffing?
Interro-negative form
Simple form
can I not biff? can you not biff? can he not biff? can we not biff? can you not biff? can they not biff?
V-ing form
can I not be biffing? can you not be biffing? can he not be biffing? can we not be biffing? can you not be biffing? can they not be biffing?
Perfect
can I not have biffed? can you not have biffed? can he not have biffed? can we not have biffed? can you not have biffed? can they not have biffed?
V-ing perfect
can I not have been biffing? can you not have been biffing? can he not have been biffing? can we not have been biffing? can you not have been biffing? can they not have been biffing?