Let there be this person X. He debates very well and can argue eloquently both "for" and "against" a particular topic. I don't exactly remember where I'd read this, but i believe there is an expression to describe such a person,something like, "he can argue both sides of the .......... ring". I cannot put my finger on what ring it was,but i vaguely remember it as having something like one side only?! please can you help me find this expression??
I don't know the exprezssion, but if it included 'either side', you'd get the singular.