I could concur you could concur she could concur we could concur you could concur they could concur
V-ing form
I could be concurring you could be concurring she could be concurring we could be concurring you could be concurring they could be concurring
Perfect
I could have concurred you could have concurred she could have concurred we could have concurred you could have concurred they could have concurred
V-ing perfect
I could have been concurring you could have been concurring she could have been concurring we could have been concurring you could have been concurring they could have been concurring
Negation
Simple form
I could not concur you could not concur she could not concur we could not concur you could not concur they could not concur
V-ing form
I could not be concurring you could not be concurring she could not be concurring we could not be concurring you could not be concurring they could not be concurring
Perfect
I could not have concurred you could not have concurred she could not have concurred we could not have concurred you could not have concurred they could not have concurred
V-ing perfect
I could not have been concurring you could not have been concurring she could not have been concurring we could not have been concurring you could not have been concurring they could not have been concurring
Interrogative form
Simple form
could I concur? could you concur? could she concur? could we concur? could you concur? could they concur?
V-ing form
could I be concurring? could you be concurring? could she be concurring? could we be concurring? could you be concurring? could they be concurring?
Perfect
could I have concurred? could you have concurred? could she have concurred? could we have concurred? could you have concurred? could they have concurred?
V-ing perfect
could I have been concurring? could you have been concurring? could she have been concurring? could we have been concurring? could you have been concurring? could they have been concurring?
Interro-negative form
Simple form
could I not concur? could you not concur? could she not concur? could we not concur? could you not concur? could they not concur?
V-ing form
could I not be concurring? could you not be concurring? could she not be concurring? could we not be concurring? could you not be concurring? could they not be concurring?
Perfect
could I not have concurred? could you not have concurred? could she not have concurred? could we not have concurred? could you not have concurred? could they not have concurred?
V-ing perfect
could I not have been concurring? could you not have been concurring? could she not have been concurring? could we not have been concurring? could you not have been concurring? could they not have been concurring?