I could lack you could lack she could lack we could lack you could lack they could lack
V-ing form
I could be lacking you could be lacking she could be lacking we could be lacking you could be lacking they could be lacking
Perfect
I could have lacked you could have lacked she could have lacked we could have lacked you could have lacked they could have lacked
V-ing perfect
I could have been lacking you could have been lacking she could have been lacking we could have been lacking you could have been lacking they could have been lacking
Negation
Simple form
I could not lack you could not lack she could not lack we could not lack you could not lack they could not lack
V-ing form
I could not be lacking you could not be lacking she could not be lacking we could not be lacking you could not be lacking they could not be lacking
Perfect
I could not have lacked you could not have lacked she could not have lacked we could not have lacked you could not have lacked they could not have lacked
V-ing perfect
I could not have been lacking you could not have been lacking she could not have been lacking we could not have been lacking you could not have been lacking they could not have been lacking
Interrogative form
Simple form
could I lack? could you lack? could she lack? could we lack? could you lack? could they lack?
V-ing form
could I be lacking? could you be lacking? could she be lacking? could we be lacking? could you be lacking? could they be lacking?
Perfect
could I have lacked? could you have lacked? could she have lacked? could we have lacked? could you have lacked? could they have lacked?
V-ing perfect
could I have been lacking? could you have been lacking? could she have been lacking? could we have been lacking? could you have been lacking? could they have been lacking?
Interro-negative form
Simple form
could I not lack? could you not lack? could she not lack? could we not lack? could you not lack? could they not lack?
V-ing form
could I not be lacking? could you not be lacking? could she not be lacking? could we not be lacking? could you not be lacking? could they not be lacking?
Perfect
could I not have lacked? could you not have lacked? could she not have lacked? could we not have lacked? could you not have lacked? could they not have lacked?
V-ing perfect
could I not have been lacking? could you not have been lacking? could she not have been lacking? could we not have been lacking? could you not have been lacking? could they not have been lacking?