One of the continuing debates in our postmodern world today is whether universals, such as justice, even exist. Though it might be argued that thinking (logical or analytic reasoning) can occur in the absence of language skills, one cannot sensibly argue that language (the realm of verbal communication) operates without symbols having definite meaning. Thus, many arguments in philosophy are believed to be mere problems in the use of language. If everyone agreed what our symbols refer to, then much confusion could be avoided.
However, in philosophy nothing should ever be assumed. Even the meanings of words we commonly take for granted. When Socrates is asked by Glaucon for a definition of justice which will satisfy everyone (i.e., true for everyone at all times and places), he cannot immediately comply. That is to say, rather than give one definition which will satisfy the question, Socrates will need to give two answers and show how they are related. First, Socrates will explain what justice means to the polis (or city); then Socrates will explain what justice means to the individual. By the end of the Republic, Socrates intends to show Glaucon how these two separate definitions are actually inseparable and, by implication, why justice in the city is invariably linked with justice in the soul of the individual.