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