I could quiver you could quiver he could quiver we could quiver you could quiver they could quiver
V-ing form
I could be quivering you could be quivering he could be quivering we could be quivering you could be quivering they could be quivering
Perfect
I could have quivered you could have quivered he could have quivered we could have quivered you could have quivered they could have quivered
V-ing perfect
I could have been quivering you could have been quivering he could have been quivering we could have been quivering you could have been quivering they could have been quivering
Negation
Simple form
I couldn't quiver you couldn't quiver he couldn't quiver we couldn't quiver you couldn't quiver they couldn't quiver
V-ing form
I couldn't be quivering you couldn't be quivering he couldn't be quivering we couldn't be quivering you couldn't be quivering they couldn't be quivering
Perfect
I couldn't have quivered you couldn't have quivered he couldn't have quivered we couldn't have quivered you couldn't have quivered they couldn't have quivered
V-ing perfect
I couldn't have been quivering you couldn't have been quivering he couldn't have been quivering we couldn't have been quivering you couldn't have been quivering they couldn't have been quivering
Interrogative form
Simple form
could I quiver? could you quiver? could he quiver? could we quiver? could you quiver? could they quiver?
V-ing form
could I be quivering? could you be quivering? could he be quivering? could we be quivering? could you be quivering? could they be quivering?
Perfect
could I have quivered? could you have quivered? could he have quivered? could we have quivered? could you have quivered? could they have quivered?
V-ing perfect
could I have been quivering? could you have been quivering? could he have been quivering? could we have been quivering? could you have been quivering? could they have been quivering?
Interro-negative form
Simple form
couldn't I quiver? couldn't you quiver? couldn't he quiver? couldn't we quiver? couldn't you quiver? couldn't they quiver?
V-ing form
couldn't I be quivering? couldn't you be quivering? couldn't he be quivering? couldn't we be quivering? couldn't you be quivering? couldn't they be quivering?
Perfect
couldn't I have quivered? couldn't you have quivered? couldn't he have quivered? couldn't we have quivered? couldn't you have quivered? couldn't they have quivered?
V-ing perfect
couldn't I have been quivering? couldn't you have been quivering? couldn't he have been quivering? couldn't we have been quivering? couldn't you have been quivering? couldn't they have been quivering?