Socrates, Plato's teacher, asks Cephalus about the experience of old age, wondering if it is a painful stage of life. Cephalus responds by saying that while some people are unhappy in old age because they miss their youth, he has encountered individuals who do not feel that way.
Cephalus recounts an encounter with Sophocles, where the poet expressed joy at having escaped the grip of love/libido/sex and other passionate desires associated with youth. Cephalus agrees with Sophocles, believing that old age brings profound tranquility and freedom from such desires. “It is like being delivered from a multitude of furious masters.” Socrates finds comfort in this perspective.
Socrates asks Cephalus, Polemarchus, and Thrasymachus to define justice.
Cephalus: justice is giving what is owed. Socrates retorts by asking that if someone has intentions to harm, should you give him the weapons owed to him?
Polemarchus: the art which gives good to friends and evil to enemies. Socrates retorts that it's immoral to harm and you can confuse enemies and friends.
Thrasymachus: justice is nothing else than the interest of the stronger. Socrates retorts that a just ruler should benefit the people just like a good doctor should benefit his patients.
Socrates claims it is to one's advantage to be just and disadvantage to be unjust, and the just man would never harm another.
Socrates' young companions, Glaucon and Adeimantus make the following claims on justice:
Justice originated from social contracts aimed at preventing individuals from suffering injustice and being unable to seek revenge.
People practice justice reluctantly and out of fear of punishment, if they had the power, they would act unjustly.
The life of an unjust person is more fulfilling compared to that of a just person. For example, in the story of Gyges, he gains immense advantages by committing injustices with the help of a ring that makes him invisible.
People value justice solely for the rewards it brings, such as fortune, honor, and reputation.
Unjust men can receive religious forgiveness by making religious sacrifices.
Socrates and his interlocutors use a luxurious city governed by a guardian class of philosopher kings as a metaphor to understand the nature of justice within an individual's soul.
The education of these guardians is examined, emphasizing the virtues of wisdom, courage, justice, and temperance, along with physical training to promote good health.
Socrates suggests that male and female guardians should receive the same education.
Socrates advocates for the communal sharing of spouses and children, as well as the prohibition of private property.
The importance of proper education in maintaining a just society is emphasized, as it shapes individuals' behavior and prevents lawlessness.
Children are raised collectively, with no knowledge of their biological parents, fostering social cohesion.
The youth are educated in works that promote self-improvement for the benefit of the state, presenting gods as entirely good and just.
In the ideal city, the philosopher-king must possess intelligence, reliability, and a willingness to lead a simple life.
A "noble lie" (that all are siblings born of the earth of the city) to create a sense of connection and belonging among citizens is necessary to develop a strong attachment to the city, leading people to protect and support it during times of conflict and peace.
The study of individuals cannot be separated from the examination of their city. Just as a city shapes its citizens, the citizens also influence and shape their city.
An individual's soul is revealed through his speeches. A city's soul is founded on its laws.
The city and soul are divided into three parts (reason, spirit, and desire), and each part of the city corresponds to a specific part of the individual's soul. In the city, reason is represented by rulers, spirit is represented by the army, and desire is represented by farmers and artists.
Socrates concludes that philosophers, who are least susceptible to corruption, should rule the ideal city. These philosopher-kings possess knowledge of the Forms (the physical world is not as real as absolute ideas) and govern for the common good, practicing sober communism and eschewing personal property and salary.
Socrates proposes that justice means responsibly fulfilling one's appropriate role, benefiting oneself and the city.
Socrates states the dangers of appearing just while being truly unjust. He compares it to a deceptive weapon-maker who produces shields that look sturdy but fail in battle. Cities with laws that benefit the few and are ruled by tyrants are inherently unjust, even if they appear just.
Socrates tells the Allegory of the Cave:
A group of prisoners is confined in a cave, unable to see the outside world. They only perceive shadows cast on the cave wall by objects illuminated by a fire. These prisoners mistake the shadows for reality and assign names to them.
When a prisoner is released and exposed to the outside world, he is initially blinded by the light but gradually perceives the true nature of objects and realizes that the shadows were mere imitations. This represents the philosopher's journey from ignorance to knowledge of the Forms.
The philosopher's duty is then to return to the cave and enlighten others, as they are best equipped to govern society based on their understanding of true goodness.
Socrates' progression of governments involves five types of regimes: aristocracy, timocracy, oligarchy, democracy, and tyranny.
It begins with an ideal aristocracy ruled by a philosopher-king, but over time, it deteriorates into timocracy when the next generation focuses on honor and wealth accumulation rather than cultivating virtues.
Timocracy is replaced by oligarchy, where the rich rule and become stringent to maintain their wealth.
As tensions between social classes grow and they clash, democracy emerges. Eventually an attractive demagogue rises to power.
Democracy eventually degenerates into tyranny, where a tyrant holds absolute power and causes chaos.
Socrates also applies these regimes to individuals and their corresponding souls. It begins with the aristocrat, who may become weak or detached from power, leading his ambitious son to become overly ambitious. This leads to the emergence of the timocrat, who seeks wealth and power to protect himself. The timocrat's son, growing up in a wealthy environment, becomes an oligarch, valuing material wealth above all else. The oligarch's son, indulged in desires, becomes a democratic individual torn between passions and discipline. He values freedom but is influenced by both good and bad desires. Finally, the democratic individual may evolve into a tyrant, driven by unrestrained desires and lacking in discipline or moderation.
Socrates concludes with The Myth of Er, a story that explores the concept of the afterlife and the consequences of one's actions in life. Er, a soldier who died in battle, is granted the opportunity to return to life and shares his account of the afterlife. He describes a journey where souls are judged and rewarded or punished based on their deeds. The just and virtuous are rewarded, while the unjust and wicked face punishments. Each soul chooses a new life, guided by a divine being, to either learn from past mistakes or continue their virtuous path. The myth emphasizes the importance of leading a just and ethical life, as it has implications not only in this world but also in the realm beyond death.