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