Plato’s Theory of Ideas and Knowledge
Philosophical Context
Plato, influenced by the Pythagoreans and the Pluralists, continues the work begun by his teacher, Socrates, concerning reality (ontology) and knowledge (epistemology). The central question was whether the principle of reality was one or many, abstract or material, divine or natural. Plato responded by establishing a radical distinction between the sensible world (the world of material beings, which is multiple and changing) and the intelligible world (the world of Ideas, which is unique, motionless, and real). The latter serves as the ontological and epistemological principle of the former. This is the famous Platonic dualism, forcing Plato to postulate two kinds of knowledge: sensory and rational. In this way, Plato synthesizes the philosophies of Heraclitus and Parmenides.
Reflecting on Socratic philosophy, Plato rejects the materialism of the Milesians and Democritus, postulating the existence of an intangible and invisible being. He agreed with Heraclitus that sensible things are subject to constant flux, but he also defended, like Parmenides, the existence of a real, permanent being, which is the object of knowledge. From the Pythagorean school, he adopted the importance of mathematics, anthropological dualism, and the doctrine of the reincarnation of the soul. He surpassed the philosophy of Parmenides, whom he considered too static and unique, and denied becoming. He refuted the Sophists by rejecting the relativity of moral values and science.
Theory of Ideas
Three main reasons led Plato to create the Theory of Ideas:
- Ethics: Against moral relativism, Plato sought an eternal and universal Idea of the Good.
- Politics: He wanted to establish a system ruled by philosopher-kings, guided by ideals and not corrupted by political life.
- Science: Science must deal with stable objects, which are the Ideas.
Ideas are unique, timeless, motionless, and accessible only to the mind. Reality and knowledge depend on them. Plato divides reality into two worlds:
- Intelligible World: Known through reason.
- Sensible World: Known through the senses.
The sensible world is a copy of the intelligible world. The relationship between these two worlds is explained through the theories of Participation and Imitation:
- Participation: Sensible beings participate in their corresponding Ideas. However, this raises the issue of how the unity of the Ideas is maintained if multiple things participate in them. It suggests the sensible world is an image of the higher world.
- Imitation: Sensible beings mimic Ideas.
In the Phaedo, Plato presents arguments for the existence of the intelligible world. The most important is Reminiscence, which states that before joining the body, the soul existed and contemplated the Ideas. This also serves as proof of the soul’s immortality. The intelligible world has a pyramid structure, with less dependent Ideas above, culminating in the Idea of the Good, which gives being to everything. In the Republic, the Idea of the Good is compared to the sun.
Theory of Knowledge
Plato’s theory of knowledge relates to the preceding arguments and aims to overcome the epistemological relativism of the Sophists. In the Republic, he distinguishes two levels of knowledge:
- Opinion (Doxa): The knowledge of sensible beings, which are material. It is divided into:
- Conjecture or Illusion: The lowest degree of knowledge, based on shadows or images of sensible beings.
- Belief: Perceptual knowledge of sensible objects.
- Wisdom (Episteme): Knowledge of Ideas:
- Demonstrative Reason: Represents mathematics, which departs from the physical and material.
- Intuitive Knowledge: The culmination of the path to wisdom, achieved through dialectical science.
The method used by Plato is dialectic. Knowledge requires effort, and therefore not all men can reach it. Only those who achieve it through love of wisdom can progress through the stages leading ultimately to intuition. Dialectics and love are the ways to ascend from the sensible world to the world of Ideas. For Plato, to know is to remember (anamnesis). This doctrine explains how a human being, existing in the world of sense, can know the world of Ideas.