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 can't concur you can't concur he can't concur we can't concur you can't concur they can't concur
V-ing form
I can't be concurring you can't be concurring he can't be concurring we can't be concurring you can't be concurring they can't be concurring
Perfect
I can't have concurred you can't have concurred he can't have concurred we can't have concurred you can't have concurred they can't have concurred
V-ing perfect
I can't have been concurring you can't have been concurring he can't have been concurring we can't have been concurring you can't have been concurring they can't 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't I concur? can't you concur? can't he concur? can't we concur? can't you concur? can't they concur?
V-ing form
can't I be concurring? can't you be concurring? can't he be concurring? can't we be concurring? can't you be concurring? can't they be concurring?
Perfect
can't I have concurred? can't you have concurred? can't he have concurred? can't we have concurred? can't you have concurred? can't they have concurred?
V-ing perfect
can't I have been concurring? can't you have been concurring? can't he have been concurring? can't we have been concurring? can't you have been concurring? can't they have been concurring?