Aporia
Aporia is the Greek term for a state of confusion or helplessness—when a person realizes they do not have a clear answer to a philosophical question. In The Republic, Socrates often leads his interlocutors to this state by questioning their beliefs. For instance, in Book 1, Socrates demonstrates that the interlocutors cannot define justice satisfactorily. While Socrates leaves them in a state of aporia, he later provides a detailed answer to the concept of justice over the next nine books.
Appetite
Appetite is the part of our soul that desires physical pleasures, like food, drink, and sex. Plato divides these desires into three categories:
- Necessary desires – desires needed for survival (e.g., hunger).
- Unnecessary desires – desires that go beyond basic needs (e.g., excessive eating or luxury foods).
- Unlawful desires – desires that go against moral principles (e.g., violent urges).
Auxiliary
In Plato’s just society, the auxiliaries are the warriors who defend the city and enforce the laws established by the guardians (the rulers). Their role is to maintain peace, protect the state from enemies, and ensure the orders of the rulers are followed. For example, in ancient times, soldiers who protect a city would be considered auxiliaries.
Belief
Belief is the second-lowest level of knowledge in Plato’s hierarchy of cognitive states. People who hold beliefs are focused on things they can see and touch, not on abstract principles. For example, someone might believe that a chair is stable because they see it and sit in it, but they do not grasp the deeper, unchanging Form of Stability.
Elenchus
Elenchus refers to the Socratic method of questioning, where Socrates asks his interlocutors a series of questions to show that their beliefs are contradictory. For instance, in Book 1 of The Republic, Socrates uses elenchus to demonstrate that the definitions of justice provided by his interlocutors are insufficient or flawed.
Empirical
An empirical question is one that can only be answered through direct observation or experience. For example, “What is the average temperature in New York in December?” requires empirical investigation, whereas “What is the sum of 2 and 2?” does not—it’s a matter of abstract reasoning.
Epistemology
Epistemology is the branch of philosophy that investigates the nature of knowledge, belief, and justification. It explores questions like: What is knowledge? How do we form beliefs? Can we ever truly know anything? In The Republic, Plato’s theory of knowledge focuses on the distinction between the visible realm (where we perceive things through senses) and the intelligible realm (where we apprehend the unchanging Forms).
Form
Plato believed that the physical world is just a shadow of a deeper, more real world—the world of the Forms. Forms are eternal, perfect, and unchanging ideals, such as the Form of Beauty or the Form of Justice. For example, an apple might be red and sweet, but its true essence—the Form of Redness and Sweetness—exists independently of any specific apple.
Form of the Good
The Form of the Good is the most important Form in Plato’s philosophy. It is the source of all other Forms and is responsible for making them intelligible. Plato compares the Form of the Good to the sun, which enables us to see and understand things. Once a philosopher understands the Form of the Good, they attain the highest level of knowledge and become capable of ruling justly, as a philosopher-king would.
Guardian
Guardians, also known as philosopher-kings, are the rulers in Plato’s ideal city. They are chosen from among the auxiliaries because they have the wisdom and knowledge to govern the city justly. A guardian must understand the Forms, especially the Form of the Good, and use that knowledge to make decisions for the good of the city. For instance, a guardian would ensure that laws are just and the needs of all citizens are met.
Hesiod
Hesiod was a Greek poet who is known for his works that discuss the nature of justice and virtue. His poem Works and Days outlines the traditional Greek view of how individuals should live a virtuous life, which Plato contrasts with his own philosophical ideas in The Republic.
Imagination
Imagination represents the lowest level of cognitive activity. Someone in the state of imagination believes that shadows and images (like art or movies) represent reality. For example, a person who only watches movies about heroism may believe that heroism is solely about physical action, rather than understanding the deeper, philosophical concept of heroism.
Instrumental Reason
Instrumental reason is the use of reason to achieve a particular goal. For instance, if someone uses logic to plan how to complete a project, they are engaging in instrumental reasoning. Plato suggests that this form of reason is important, but it is not the highest use of reason, as it is often guided by desires like appetite or spirit.
Intelligible Realm
The intelligible realm is the domain of the Forms, which are eternal and unchanging. It cannot be perceived with our senses, but only understood through reason and intellect. For example, while we can see many beautiful things in the world, the true beauty is the Form of Beauty, which exists beyond physical objects.
Kallipolis
Kallipolis is the Greek term for Plato’s ideal city. It is a city governed by philosopher-kings, where each class of people—producers, auxiliaries, and guardians—plays their proper role. The goal of this city is justice, which is achieved when everyone does the work they are naturally suited for.
Knowledge
Plato defines knowledge as true belief that is justified by understanding the unchanging Forms. For example, knowing that “2 + 2 = 4” is a form of knowledge, because it is a truth that is not subject to change. In contrast, opinions are based on sensory experiences and are not as reliable as knowledge.
Lover of Sights and Sounds
This term refers to people who focus only on the beauty of physical things (e.g., art, music, or movies) without understanding the deeper Forms that cause these things to be beautiful. For example, someone who enjoys art for its aesthetic qualities but doesn’t consider the philosophical implications of beauty would be considered a lover of sights and sounds.
Metaphysics
Metaphysics is the branch of philosophy that explores the nature of reality. It deals with questions such as: What exists? What is the nature of being? Plato’s theory of the Forms is a metaphysical theory because it explains the true nature of reality, which is beyond the physical world.
Opinion
In Plato’s philosophy, opinion is a belief that is based on sensory experiences, not on understanding the Forms. Opinion is less certain than knowledge. For example, a person might have the opinion that a flower is beautiful because they see it, but this opinion is not as reliable as the knowledge of the Form of Beauty itself.
Philosopher-king
A philosopher-king is a ruler who has knowledge of the Forms and the Form of the Good, making them the wisest and most just person to govern. Plato argues that only philosopher-kings can create a just society, as they understand true justice and can rule accordingly.
Pleonexia
Pleonexia refers to the desire for more—specifically, the desire for excessive wealth or power. In The Republic, Thrasymachus suggests that this desire is a natural part of human nature, and that justice is merely a social construct that restrains this desire.
Producers
Producers are the workers in Plato’s ideal society, responsible for creating goods and services. They are the largest class and include farmers, craftsmen, doctors, merchants, and other professionals. They focus on production, while the rulers (guardians) govern and the auxiliaries defend the city.
Reason
Reason is the part of our soul that seeks truth and knowledge. It is the highest part of the soul, and in a just person, reason governs the other parts of the soul. For example, a just individual will make decisions based on rational thought, rather than giving in to desires like appetite or spirit.
Sensible Particular
Sensible particulars are the objects we can perceive with our senses—such as trees, cars, or houses. These objects are constantly changing, unlike the unchanging Forms. For example, an apple is a sensible particular, but the Form of Redness or the Form of Sweetness is a perfect, unchanging ideal.
The Sophists
Sophists were teachers in ancient Greece who claimed to teach success in life and public speaking. They often rejected the idea of objective truth, believing that knowledge and morality were relative. Plato disagrees with the Sophists and seeks to prove that objective truth and knowledge are real.
Specialization
Specialization is the idea that everyone should do the work they are naturally best suited for. In Plato’s ideal city, those who are best at farming should farm, those best at ruling should govern, and those best at fighting should be warriors. This division of labor ensures that each person contributes to the overall good of society.
Spirit
Spirit is the part of our soul that drives us to seek honor, glory, and victory. It is also responsible for feelings of indignation and anger. In a just person, spirit works with reason to control appetite, ensuring that the individual’s desires are in harmony with their higher rational goals.
Thought
Thought is the second-highest form of cognitive activity. It involves using images and hypotheses to explore abstract concepts, but it still relies on unproven assumptions. Thought is closer to knowledge than belief, but it is not as pure as understanding, which is based solely on reason.
Tripartite Soul
Plato divides the soul into three parts: reason, spirit, and appetite. A just soul is one where reason rules, spirit supports reason, and appetite obeys. In a just society, each class (guardians, auxiliaries, producers) mirrors this structure.
Understanding
Understanding is the highest form of cognitive activity, where the mind grasps abstract, unchanging truths. It requires a complete understanding of the Forms, especially the Form of the Good. For example, someone who understands the Form of Justice grasps true justice, not just its physical manifestations.
Visible Realm
The visible realm is the world we experience through our senses. It is made up of sensible particulars, such as trees, buildings, and animals. Plato considers the visible realm to be less real than the intelligible realm, which consists of the Forms.