Plato’s Philosophy: Ideas, Knowledge, and Justice
Theory of Ideas
In his conception of reality, Plato distinguishes two worlds: the world of Ideas and the world of sensible things.
The world of Ideas is truly real and significant. It is composed of things that show us the way and are copies of Ideas. Ideas are the principle of reality because, without them, things would have no true existence. They are archetypes or models from which the Demiurge constructs the sensible world. Therefore, sensible things exist because they mimic the Ideas.
These two worlds are composed of entities with conflicting characteristics. While Ideas are unique, timeless, and immaterial, sensible things are multiple, perishable, and material. These characteristics explain the dependence of things on Ideas. The multiplicity and change of things in the sensible world are based on the unity and permanence of Ideas. For example, the infinite variety of people we know in the sensible world exists because they are copies of the Idea of ‘person’ or ‘human being’, which is unique and unchanging. The Idea gives things their being, essence, and the possibility of knowing them.
Furthermore, there is a hierarchy in the world of Ideas. From its lowest level, consisting of mathematical ideas, through ideas such as beauty and justice, this order culminates in the Idea of the Good, which is the origin and principle of all other Ideas. Plato compared the Idea of the Good to the sun in the sensible world, as it gives life to both material and immaterial things. Therefore, the Good is the ultimate principle of reality and the foundation of knowledge.
Knowledge
Plato believed that the Sophists’ argument that knowledge is a reflection of appearances is false. True knowledge requires a systematic approach that leads us through dialectic to the knowledge of Ideas.
Considering the division between the world of Ideas and the sensible world, Plato distinguishes two types of knowledge: science and opinion. Science seeks knowledge of Ideas, leading to absolute and undoubted truth. On the contrary, opinion refers to the realm of the changeable and perishable, making it unreliable and variable.
Within science, different degrees correspond to the hierarchical structure of the world of Ideas. These range from the knowledge of mathematical ideas, or discursive thought that starts from hypotheses and relies on material elements, to the knowledge of other Ideas, culminating in the Idea of the Good through dialectics. There are also two levels of knowledge of the sensible – conjecture and belief – although both are unsafe. True knowledge is that of Ideas.
To justify how humans can access the world of Ideas if they are, as told in the myth of the cave, inserted in the sensible world and unaware of the intelligible world, Plato proposes his theory of reminiscence.
To understand this theory, we must first grasp Plato’s conception of man. Man is a dual reality, a confluence of the world of Ideas and the sensible world: the accidental unity of body and soul. The body belongs to the sensible world, while the soul belongs to the world of Ideas. When the soul is incarnated in the body, it forgets the existence of the world of Ideas and falls into ignorance. The body becomes the prison of the soul. However, the soul inherently knows the Ideas, even though it has forgotten them after its union with the body.
It is necessary to undertake a path based on the observation of sensible things to awaken the soul’s remembrance of the Ideas, leading to the Idea of the Good. Knowledge is not learning new things but remembering those that were already known.
Ethics and Politics
Plato’s ethics and politics can be explained through the concept of justice. If man is the union of soul and body, we can distinguish three parts within the soul: reason, spirit, and appetite. Justice in the individual consists in the harmony of these three parts: reason dominates appetite, controlling human desires and pleasures, with the help of spirit, which is the force that aids reason in its control.
At the state level, this division of the individual soul is reflected in social classes. Each class plays a specific role: the rulers are philosophers because they know the Idea of the Good; the guardians defend the city and maintain order; and the producers create the goods necessary for subsistence. Justice is the harmony of the social classes, where each fulfills its function.
Aristocracy, meaning the government of the wise, is the perfect form of state. Its degeneration is timocracy, or the government of ambition, which further degenerates into oligarchy, or the government of the wealthy. Oligarchy, in turn, degenerates into democracy, where excessive liberty leads to tyranny, which eliminates freedom and truth.