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