I could guard you could guard she could guard we could guard you could guard they could guard
V-ing form
I could be guarding you could be guarding she could be guarding we could be guarding you could be guarding they could be guarding
Perfect
I could have guarded you could have guarded she could have guarded we could have guarded you could have guarded they could have guarded
V-ing perfect
I could have been guarding you could have been guarding she could have been guarding we could have been guarding you could have been guarding they could have been guarding
Negation
Simple form
I couldn't guard you couldn't guard she couldn't guard we couldn't guard you couldn't guard they couldn't guard
V-ing form
I couldn't be guarding you couldn't be guarding she couldn't be guarding we couldn't be guarding you couldn't be guarding they couldn't be guarding
Perfect
I couldn't have guarded you couldn't have guarded she couldn't have guarded we couldn't have guarded you couldn't have guarded they couldn't have guarded
V-ing perfect
I couldn't have been guarding you couldn't have been guarding she couldn't have been guarding we couldn't have been guarding you couldn't have been guarding they couldn't have been guarding
Interrogative form
Simple form
could I guard? could you guard? could she guard? could we guard? could you guard? could they guard?
V-ing form
could I be guarding? could you be guarding? could she be guarding? could we be guarding? could you be guarding? could they be guarding?
Perfect
could I have guarded? could you have guarded? could she have guarded? could we have guarded? could you have guarded? could they have guarded?
V-ing perfect
could I have been guarding? could you have been guarding? could she have been guarding? could we have been guarding? could you have been guarding? could they have been guarding?
Interro-negative form
Simple form
couldn't I guard? couldn't you guard? couldn't she guard? couldn't we guard? couldn't you guard? couldn't they guard?
V-ing form
couldn't I be guarding? couldn't you be guarding? couldn't she be guarding? couldn't we be guarding? couldn't you be guarding? couldn't they be guarding?
Perfect
couldn't I have guarded? couldn't you have guarded? couldn't she have guarded? couldn't we have guarded? couldn't you have guarded? couldn't they have guarded?
V-ing perfect
couldn't I have been guarding? couldn't you have been guarding? couldn't she have been guarding? couldn't we have been guarding? couldn't you have been guarding? couldn't they have been guarding?