I can howl you can howl he can howl we can howl you can howl they can howl
V-ing form
I can be howling you can be howling he can be howling we can be howling you can be howling they can be howling
Perfect
I can have howled you can have howled he can have howled we can have howled you can have howled they can have howled
V-ing perfect
I can have been howling you can have been howling he can have been howling we can have been howling you can have been howling they can have been howling
Negation
Simple form
I cannot howl you cannot howl he cannot howl we cannot howl you cannot howl they cannot howl
V-ing form
I cannot be howling you cannot be howling he cannot be howling we cannot be howling you cannot be howling they cannot be howling
Perfect
I cannot have howled you cannot have howled he cannot have howled we cannot have howled you cannot have howled they cannot have howled
V-ing perfect
I cannot have been howling you cannot have been howling he cannot have been howling we cannot have been howling you cannot have been howling they cannot have been howling
Interrogative form
Simple form
can I howl? can you howl? can he howl? can we howl? can you howl? can they howl?
V-ing form
can I be howling? can you be howling? can he be howling? can we be howling? can you be howling? can they be howling?
Perfect
can I have howled? can you have howled? can he have howled? can we have howled? can you have howled? can they have howled?
V-ing perfect
can I have been howling? can you have been howling? can he have been howling? can we have been howling? can you have been howling? can they have been howling?
Interro-negative form
Simple form
can I not howl? can you not howl? can he not howl? can we not howl? can you not howl? can they not howl?
V-ing form
can I not be howling? can you not be howling? can he not be howling? can we not be howling? can you not be howling? can they not be howling?
Perfect
can I not have howled? can you not have howled? can he not have howled? can we not have howled? can you not have howled? can they not have howled?
V-ing perfect
can I not have been howling? can you not have been howling? can he not have been howling? can we not have been howling? can you not have been howling? can they not have been howling?