By the end of Book I of the Republic, Thrasymachus has been pretty much silenced. Later in the work he will raise his voice a few times again, but only to agree, more wholeheartedly, with Socrates. But although Thrasymachus has been equalled, if not beaten at his own game, the company of discussants is not satisfied with Socrates" answer so far. Thrasymachus" problem (at least Socrates" version of it) still stands.
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At this point Adeimantus and Glaucon (the names of two of Plato's actual brothers) raise the issue again, and in a new, clearer form. Glaucon agrees with Thrasymachus that there does indeed seem to be something unnatural about justice, although he will not state, like Thrasymachus, that justice is the interest of the stronger. According to Glaucon, in a state of nature men inflict and suffer injustice without restraint. That is simply how human beings are, according to the view he is putting forward. States and common laws exist due to an agreement among those who are relatively weak. It is they who contract with one another not to do injustice or allow it to be done. Glaucon is here offering the inverse of Thrasymachus" argument, by claiming, although he does not put it explicitly in these terms, that justice is the interest of the weak. He is saying that justice is a convention and therefore unnatural. Its existence does not benefit the relatively few strong individuals. It benefits the relatively many weak, who would not practice justice if they could get away with ignoring it. According to Glaucon, human nature tends strongly, if not exclusively, towards a desire for self-aggrandizement that really knows no inherent limits. For him, the strong individual has no obligation to uphold the law of the community, and he will grant that if justice is good at all, it is only good instrumentally, as a means to something else. The apparently inevitable conclusion is that the best man (and the one who lives best) would be the one who appears to be just, but manages to practice injustice when it suits his purposes.
