I could stammer you could stammer he could stammer we could stammer you could stammer they could stammer
V-ing form
I could be stammering you could be stammering he could be stammering we could be stammering you could be stammering they could be stammering
Perfect
I could have stammered you could have stammered he could have stammered we could have stammered you could have stammered they could have stammered
V-ing perfect
I could have been stammering you could have been stammering he could have been stammering we could have been stammering you could have been stammering they could have been stammering
Negation
Simple form
I could not stammer you could not stammer he could not stammer we could not stammer you could not stammer they could not stammer
V-ing form
I could not be stammering you could not be stammering he could not be stammering we could not be stammering you could not be stammering they could not be stammering
Perfect
I could not have stammered you could not have stammered he could not have stammered we could not have stammered you could not have stammered they could not have stammered
V-ing perfect
I could not have been stammering you could not have been stammering he could not have been stammering we could not have been stammering you could not have been stammering they could not have been stammering
Interrogative form
Simple form
could I stammer? could you stammer? could he stammer? could we stammer? could you stammer? could they stammer?
V-ing form
could I be stammering? could you be stammering? could he be stammering? could we be stammering? could you be stammering? could they be stammering?
Perfect
could I have stammered? could you have stammered? could he have stammered? could we have stammered? could you have stammered? could they have stammered?
V-ing perfect
could I have been stammering? could you have been stammering? could he have been stammering? could we have been stammering? could you have been stammering? could they have been stammering?
Interro-negative form
Simple form
could I not stammer? could you not stammer? could he not stammer? could we not stammer? could you not stammer? could they not stammer?
V-ing form
could I not be stammering? could you not be stammering? could he not be stammering? could we not be stammering? could you not be stammering? could they not be stammering?
Perfect
could I not have stammered? could you not have stammered? could he not have stammered? could we not have stammered? could you not have stammered? could they not have stammered?
V-ing perfect
could I not have been stammering? could you not have been stammering? could he not have been stammering? could we not have been stammering? could you not have been stammering? could they not have been stammering?