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