Plato’s Republic (c. 380 BCE) is a dialogue in which Socrates and his interlocutors discuss the attributes and virtues that make for the most just person and for the most just form of government. The Republic also examines the relationship between the citizen and the city, and considers how this relationship bears on philosophy, politics, ethics and art.
How do you define justice? No matter how well considered your response may be, Socrates would probably be able to dismantle your definition. Throughout the dialogue between him and his interlocutors, he examines and questions several definitions of justice.
The first definition comes from Polemarchus, who claims that justice is to give each person what they are owed. In response, Socrates tries to undermine this definition by finding exceptions to it. What if weapons are owed? Although one should return what one owes, one should not offer weapons to someone who is insane and threatening to harm someone.
So, the definition of justice as “giving what is owed” doesn’t always hold.
Polemarchus then provides another answer: Being just means assisting friends and harming enemies. To this, Socrates queries whether there are circumstances under which it is moral to do harm. He finds that there aren’t. Animal trainers, he says, don’t benefit animals they harm; likewise, people become less moral if harmed. Additionally, one can mistake friends for enemies, and enemies for friends, and therefore end up benefiting those one meant to harm.
So, since harming someone isn’t beneficial and our judgments cannot be absolutely accurate, this second definition also falls apart.
The third definition, posited by Thrasymachus, is that justice is whatever is advantageous to the ruler.
Socrates questions whether this definition also applies to those in other positions – such as, say, a doctor. The health of the patient, rather than the doctor’s benefit, should be the doctor’s main concern. A ruler that seeks to benefit himself, instead of his people, is not a just ruler. Like the doctor, the ruler should aim to do good for his “patient,” i.e., the city.
This third definition is also inadequate and so the first attempts to define justice come to an aporia, an impasse in the dialogue.