Plato’s Dualism: Sensible vs. Intelligible Worlds
Plato’s Theory of Forms
According to Plato, Heraclitus would have argued that sensible objects are subject to constant change and various movements that make it impossible for something to be equal to itself. Parmenides believed that plurality and change were deceptive appearances of sense, and that being, the authentic fact, is ungenerated, homogenous, immutable, and imperishable. On the other hand, the Sophists advocated epistemological skepticism and relativism. Plato shows us a Socrates who seeks the definition of moral terms that express the permanent essence of each concept.
In all this, Plato believes that knowledge must be absolute, universal, and infallible, and we must aim for true reality. We cannot deny the evidence that we can only have true knowledge of what does not change, what has always remained stable and identical to itself. The solution is to affirm the existence of two different worlds with their alterations: the sensible world and the intelligible world, which consists of eternal and immutable realities that can only be grasped by the intellect. The sensible world is the world of objects we perceive through the senses. Objects are subject to various changes and alterations; therefore, it cannot be said that they properly belong to the intelligible world.
The World of Ideas
The ideas represent the higher level of reality; they are eternal, immutable, permanent, and identical to themselves. All these ideas are hierarchically organized, and on top of them all is the idea of Good that represents the order and meaning of all reality.
Levels of Knowledge
Corresponding to the different degrees of reality, there are different levels of knowledge: opinion, which refers to sensible objects, and episteme, which refers to intelligible objects such as ideas. Things that are changing do not allow true knowledge, only opinion, which is somewhat darker than brighter knowledge but not ignorance. Among them, only superficial knowledge is possible because of reality changing and unstable; when we believe we have captured it, it has changed. Because the senses with which we agree to them are not reliable tools of knowledge, only the truly real, Ideas, make absolute knowledge possible, objective, and universal.
The Epistemological Problem
The opposition between both worlds poses an epistemological problem: if the true reality is separate from the physical world, but our experience is immediately of sensible objects, how can we gain knowledge of it? Plato uses myth to explain this issue. The myth suggests that the sensible world was created modeled on the world of ideas, things that imitate or participate in the perfect models that are ideas. If man’s attitude is right, if his gaze is rightly directed, things may suggest ideas.
Ontological and Epistemological Dualism
The theory of ideas is the most original of Platonic philosophy and involves the distinction between two levels of reality, what is called ontological dualism, and their two levels of knowledge, called epistemological dualism. Regarding the sensible world, we can only have opinion. The level of what is really real is the intelligible world, also called the world of ideas. Only such knowledge can be strictly true.