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