There is a difference between a citizen and a subject. Roughly, a citizen holds some power in the state (through voting or otherwise), whereas a subject is subordinate to their leader and has no say. (I hope I'm using the standard terminology here. I mean the Finnish words "kansalainen" and "alamainen".) My dictionary indicates that the terms "citizen" and "subject" are civis and subiectus in Latin. This sounds legitimate, but I failed to find any classical comparisons of the two terms.
I would like to know how these words compared to each other in classical Latin — or later Latin if the distinction was not clear in antiquity. Are there any classical comparisons of the two terms? Or should the opposing pair corresponding to "citizen" and "subject" be something other than civis and subiectus? If there is nothing classical, how about later ones? I would prefer if the two were explicitly compared, but separate clear definitions are also fine if found somewhere.