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