Plato’s Theory of Ideas: Exploring the Sensible and Intelligible
Plato’s Theory of Ideas
The Two Realities
Plato’s philosophy centers on the Theory of Ideas, which distinguishes two modes of reality. The intelligible world, or World of Ideas, is intangible, eternal, and indestructible—unchanging and serving as the model for the second reality. This second reality, the sensible world, consists of tangible, corruptible things, mere copies of the intelligible reality.
The Ideas represent true being, while material realities are in constant flux. True knowledge, or episteme, is only attainable through the Ideas. Sensible reality only allows for opinion, or doxa. Works like the Phaedo and the Timaeus highlight this separation between the sensible and the intelligible.
Ideas as Essences
Ideas represent the essences of objects of knowledge. They are not mental contents themselves, but rather the objects to which mental contents refer. These Ideas are unique, eternal, immutable, and knowable only through reason. They are not material and exist independently of both the subject and the object of thought. The sensible reality imitates or participates in these Ideas.
The sensible reality is characterized by change, mobility, generation, and corruption.
Dialectic and the Levels of Knowledge
In Book VI of the Republic, Plato introduces the dialectic, linking levels of reality with levels of knowledge. He distinguishes between doxa (sensible knowledge) and episteme (intelligible knowledge). True knowledge, episteme, concerns being and is infallible. It is achieved through knowledge of the Ideas.
The Simile of the Line
Plato uses the simile of a divided line to illustrate this. The line represents the sensible and intelligible domains. The sensible part is divided into images of material objects (shadows, reflections) and the things themselves. The intelligible part is divided into images (logical and mathematical objects) and the Ideas themselves.
- Eikasia (Imagination): Misleading representations from images of material objects.
- Pistis (Belief): More accurate representations from material objects.
- Dianoia (Discursive Knowledge): Knowledge from images of Ideas (mathematical objects).
- Noesis (Intellectual Knowledge): Knowledge of the Ideas themselves.
Dianoia and noesis differ in their objects and characteristics. Dianoia assumes the existence of its objects of study. Mathematicians use sensible images to aid their arguments. Noesis, however, uses only abstract and universal Ideas. Mathematicians reach conclusions based on assumptions, while the dialectic’s conclusion is a principle—the Idea of the Good—which is the beginning of everything.