Final answer:
Socrates explains to Adeimantus how justice and injustice work individually by using the analogy of the just city and arguing that a just man is more successful and happier than an unjust man.
Step-by-step explanation:
Socrates explains to Adeimantus how justice and injustice work individually by illustrating it through the analogy of the just city. He argues that a just city, where each member fulfills their role and works for the good of the society, is more successful than an unjust one. Therefore, he concludes that a just man will be more successful and happier than an unjust man. Socrates believes that behaving justly and fulfilling one's duties leads to internal harmony and goodness in both individuals and society.