In order to satisfy his own philosophical goals and to appease Callicles, Socrates next focuses on the nature of justice. For Callicles, justice is natural justice: the more powerful control the less so by means of force, and the better rule over the worse. He himself considers the powerful and the better to be equivalent, but he also agrees with Socrates that the majority of humans believe justice means equal shares for all. This includes equality of opportunity, safety, and punishment for example. Everything the noble and powerful are entitled to, so too are the base and weak entitled under a just system. (For Plato's extended definition of a truly good and just state, see ##The Republic.##)
In order to oppose Callicles's definition of justice as natural justice (the powerful rule the weak), and amidst a brief flurry of renewed insults directed at him by Callicles, Socrates offers the example of a slave being better than his or her owner as a result of possessing greater strength. Surely, Callicles would not allow that a person as base as a slave should rule over their weaker slave owner based solely upon the merit of the increased strength that most likely naturally accompanies the extended and difficult physical labor normal to a slave's daily existence. As a result, Callicles offers a revised definition of natural justice, namely that the better and wiser rule over and possess more than the inferior.
Callicles's formulation prompts Socrates to shift into an examination of whether such rulers (and all other humans) are in control of themselves. This inquiry introduces the concept of temperance; "mastering one's own pleasures and appetites." Callicles subsequently states his distaste for temperance, choosing instead to maintain that happiness and power result from ridding one's desires of all restraint, and allowing them to grow without limitation. He sees temperance as a sign of weakness. Socrates immediately responds with the metaphor of a leaky jar, which illustrates that a soul with unrestrained desires will always require more and more (and thus never be complete), just as a jar with large holes could never remain full. For Socrates, justice equals temperance of the soul and its desires.
Callicles, however, remains unconvinced. He declares that a full jar allows no room for more pleasure, and therefore that temperance and restraint are undesirable. Socrates harbors serious doubt about this equation of the good with pleasure. He continues on by establishing that an appetite or deficiency such as thirst is painful, while eating is a satisfaction of this deficiency and therefore a pleasure. When a person eats to satisfy her hunger, then, she simultaneously experiences both pleasure and pain. It is not possible, though, to be both faring well (a good) and faring poorly (an evil) at the same time. Thus, because, when one eats, bodily pleasure and pain exist concurrently, against the fact that one cannot at once fare both well and poorly, it follows logically that the pleasure is not equivalent to the good, nor is pain synonymous with evil. Callicles concurs.
The conception of justice offered here by Callicles appears to represent a prevalent definition of that notion within Plato's Athenian society. This is so since the corrupt government in power at the time itself serves as a model of the strong and aggressive dominating the weak. Amidst decades of significant internal strife, the resulting Athenian power vacuum enabled those with the proper force and requisite assertion of this force to take control and implement their own laws of engagement within society. A direct translation of power into law and authority perfectly encapsulates Socrates's contemporaries' outlining of justice. This exactly is what happened following the Peloponnesian War, when a group of corrupt wealthy opportunists seized authority for their own gain. Thus, by utilizing Callicles to state the case as such, Plato establishes the dominant belief he intends his current strain of inquiry to destroy.
The leaky jar imagery provides a concise and vivid refutation of the notion that happiness resides in the freedom of one's desires to grow without limitation. Intuition again runs counter to Socrates's line of reasoning, since human instinct almost automatically desires ultimate pleasure. Such an approach, however, remains mired in the equation of the good with the pleasant. Plato's implementation of metaphor in order to illustrate his argument allows him much more clearly to express the main claim of this section in terms accessible even to those who do not already desire the temperance of their appetites. Put differently, it is one thing for a man such as Plato, who is already convinced of the desirability of virtue and restraint, to argue in favor of temperance rather than support of desire in its general sense and specific instantiations. But it is something else entirely for someone not approaching the text from a position of agreement with Socrates's claims (such as Callicles, or a modern college student) to be convinced of this view, either in the abstract or in particular instances of it. By framing the discussion within such vivid imagery, however, the thrust and logic of his point becomes undeniable, even for his biggest opponent.