I could billow you could billow she could billow we could billow you could billow they could billow
V-ing form
I could be billowing you could be billowing she could be billowing we could be billowing you could be billowing they could be billowing
Perfect
I could have billowed you could have billowed she could have billowed we could have billowed you could have billowed they could have billowed
V-ing perfect
I could have been billowing you could have been billowing she could have been billowing we could have been billowing you could have been billowing they could have been billowing
Negation
Simple form
I could not billow you could not billow she could not billow we could not billow you could not billow they could not billow
V-ing form
I could not be billowing you could not be billowing she could not be billowing we could not be billowing you could not be billowing they could not be billowing
Perfect
I could not have billowed you could not have billowed she could not have billowed we could not have billowed you could not have billowed they could not have billowed
V-ing perfect
I could not have been billowing you could not have been billowing she could not have been billowing we could not have been billowing you could not have been billowing they could not have been billowing
Interrogative form
Simple form
could I billow? could you billow? could she billow? could we billow? could you billow? could they billow?
V-ing form
could I be billowing? could you be billowing? could she be billowing? could we be billowing? could you be billowing? could they be billowing?
Perfect
could I have billowed? could you have billowed? could she have billowed? could we have billowed? could you have billowed? could they have billowed?
V-ing perfect
could I have been billowing? could you have been billowing? could she have been billowing? could we have been billowing? could you have been billowing? could they have been billowing?
Interro-negative form
Simple form
could I not billow? could you not billow? could she not billow? could we not billow? could you not billow? could they not billow?
V-ing form
could I not be billowing? could you not be billowing? could she not be billowing? could we not be billowing? could you not be billowing? could they not be billowing?
Perfect
could I not have billowed? could you not have billowed? could she not have billowed? could we not have billowed? could you not have billowed? could they not have billowed?
V-ing perfect
could I not have been billowing? could you not have been billowing? could she not have been billowing? could we not have been billowing? could you not have been billowing? could they not have been billowing?