I should back you should back she should back we should back you should back they should back
V-ing form
I should be backing you should be backing she should be backing we should be backing you should be backing they should be backing
Perfect
I should have backed you should have backed she should have backed we should have backed you should have backed they should have backed
V-ing perfect
I should have been backing you should have been backing she should have been backing we should have been backing you should have been backing they should have been backing
Negation
Simple form
I should not back you should not back she should not back we should not back you should not back they should not back
V-ing form
I should not be backing you should not be backing she should not be backing we should not be backing you should not be backing they should not be backing
Perfect
I should not have backed you should not have backed she should not have backed we should not have backed you should not have backed they should not have backed
V-ing perfect
I should not have been backing you should not have been backing she should not have been backing we should not have been backing you should not have been backing they should not have been backing
Interrogative form
Simple form
should I back? should you back? should she back? should we back? should you back? should they back?
V-ing form
should I be backing? should you be backing? should she be backing? should we be backing? should you be backing? should they be backing?
Perfect
should I have backed? should you have backed? should she have backed? should we have backed? should you have backed? should they have backed?
V-ing perfect
should I have been backing? should you have been backing? should she have been backing? should we have been backing? should you have been backing? should they have been backing?
Interro-negative form
Simple form
should I not back? should you not back? should she not back? should we not back? should you not back? should they not back?
V-ing form
should I not be backing? should you not be backing? should she not be backing? should we not be backing? should you not be backing? should they not be backing?
Perfect
should I not have backed? should you not have backed? should she not have backed? should we not have backed? should you not have backed? should they not have backed?
V-ing perfect
should I not have been backing? should you not have been backing? should she not have been backing? should we not have been backing? should you not have been backing? should they not have been backing?