I could understand you could understand she could understand we could understand you could understand they could understand
V-ing form
I could be understanding you could be understanding she could be understanding we could be understanding you could be understanding they could be understanding
Perfect
I could have understood you could have understood she could have understood we could have understood you could have understood they could have understood
V-ing perfect
I could have been understanding you could have been understanding she could have been understanding we could have been understanding you could have been understanding they could have been understanding
Negation
Simple form
I could not understand you could not understand she could not understand we could not understand you could not understand they could not understand
V-ing form
I could not be understanding you could not be understanding she could not be understanding we could not be understanding you could not be understanding they could not be understanding
Perfect
I could not have understood you could not have understood she could not have understood we could not have understood you could not have understood they could not have understood
V-ing perfect
I could not have been understanding you could not have been understanding she could not have been understanding we could not have been understanding you could not have been understanding they could not have been understanding
Interrogative form
Simple form
could I understand? could you understand? could she understand? could we understand? could you understand? could they understand?
V-ing form
could I be understanding? could you be understanding? could she be understanding? could we be understanding? could you be understanding? could they be understanding?
Perfect
could I have understood? could you have understood? could she have understood? could we have understood? could you have understood? could they have understood?
V-ing perfect
could I have been understanding? could you have been understanding? could she have been understanding? could we have been understanding? could you have been understanding? could they have been understanding?
Interro-negative form
Simple form
could I not understand? could you not understand? could she not understand? could we not understand? could you not understand? could they not understand?
V-ing form
could I not be understanding? could you not be understanding? could she not be understanding? could we not be understanding? could you not be understanding? could they not be understanding?
Perfect
could I not have understood? could you not have understood? could she not have understood? could we not have understood? could you not have understood? could they not have understood?
V-ing perfect
could I not have been understanding? could you not have been understanding? could she not have been understanding? could we not have been understanding? could you not have been understanding? could they not have been understanding?