I could sit you could sit she could sit we could sit you could sit they could sit
V-ing form
I could be sitting you could be sitting she could be sitting we could be sitting you could be sitting they could be sitting
Perfect
I could have sat you could have sat she could have sat we could have sat you could have sat they could have sat
V-ing perfect
I could have been sitting you could have been sitting she could have been sitting we could have been sitting you could have been sitting they could have been sitting
Negation
Simple form
I could not sit you could not sit she could not sit we could not sit you could not sit they could not sit
V-ing form
I could not be sitting you could not be sitting she could not be sitting we could not be sitting you could not be sitting they could not be sitting
Perfect
I could not have sat you could not have sat she could not have sat we could not have sat you could not have sat they could not have sat
V-ing perfect
I could not have been sitting you could not have been sitting she could not have been sitting we could not have been sitting you could not have been sitting they could not have been sitting
Interrogative form
Simple form
could I sit? could you sit? could she sit? could we sit? could you sit? could they sit?
V-ing form
could I be sitting? could you be sitting? could she be sitting? could we be sitting? could you be sitting? could they be sitting?
Perfect
could I have sat? could you have sat? could she have sat? could we have sat? could you have sat? could they have sat?
V-ing perfect
could I have been sitting? could you have been sitting? could she have been sitting? could we have been sitting? could you have been sitting? could they have been sitting?
Interro-negative form
Simple form
could I not sit? could you not sit? could she not sit? could we not sit? could you not sit? could they not sit?
V-ing form
could I not be sitting? could you not be sitting? could she not be sitting? could we not be sitting? could you not be sitting? could they not be sitting?
Perfect
could I not have sat? could you not have sat? could she not have sat? could we not have sat? could you not have sat? could they not have sat?
V-ing perfect
could I not have been sitting? could you not have been sitting? could she not have been sitting? could we not have been sitting? could you not have been sitting? could they not have been sitting?