I could agree you could agree he could agree we could agree you could agree they could agree
V-ing form
I could be agreeing you could be agreeing he could be agreeing we could be agreeing you could be agreeing they could be agreeing
Perfect
I could have agreed you could have agreed he could have agreed we could have agreed you could have agreed they could have agreed
V-ing perfect
I could have been agreeing you could have been agreeing he could have been agreeing we could have been agreeing you could have been agreeing they could have been agreeing
Negation
Simple form
I couldn't agree you couldn't agree he couldn't agree we couldn't agree you couldn't agree they couldn't agree
V-ing form
I couldn't be agreeing you couldn't be agreeing he couldn't be agreeing we couldn't be agreeing you couldn't be agreeing they couldn't be agreeing
Perfect
I couldn't have agreed you couldn't have agreed he couldn't have agreed we couldn't have agreed you couldn't have agreed they couldn't have agreed
V-ing perfect
I couldn't have been agreeing you couldn't have been agreeing he couldn't have been agreeing we couldn't have been agreeing you couldn't have been agreeing they couldn't have been agreeing
Interrogative form
Simple form
could I agree? could you agree? could he agree? could we agree? could you agree? could they agree?
V-ing form
could I be agreeing? could you be agreeing? could he be agreeing? could we be agreeing? could you be agreeing? could they be agreeing?
Perfect
could I have agreed? could you have agreed? could he have agreed? could we have agreed? could you have agreed? could they have agreed?
V-ing perfect
could I have been agreeing? could you have been agreeing? could he have been agreeing? could we have been agreeing? could you have been agreeing? could they have been agreeing?
Interro-negative form
Simple form
couldn't I agree? couldn't you agree? couldn't he agree? couldn't we agree? couldn't you agree? couldn't they agree?
V-ing form
couldn't I be agreeing? couldn't you be agreeing? couldn't he be agreeing? couldn't we be agreeing? couldn't you be agreeing? couldn't they be agreeing?
Perfect
couldn't I have agreed? couldn't you have agreed? couldn't he have agreed? couldn't we have agreed? couldn't you have agreed? couldn't they have agreed?
V-ing perfect
couldn't I have been agreeing? couldn't you have been agreeing? couldn't he have been agreeing? couldn't we have been agreeing? couldn't you have been agreeing? couldn't they have been agreeing?