Plato’s Dualism: Knowledge of Two Realities
The Problem of Knowledge in a Changing World
Are there two types of knowledge corresponding to two types of reality? According to Heraclitus, everything in nature flows. Plato argues from this that if nature is constantly changing, it is impossible to validate a claim forever; any claim only applies to a single instant. The skeptic Gorgias stated that we know only appearances, that a permanent reality does not exist, and that even if it did and someone could grasp it, they could not communicate it to others.
Furthermore, the Sophists aimed to convince rather than find truth, making validity relative. For them, what is considered valid, fair, or good depends on the majority’s view. This approach, Plato believed, could not lead to a just government. Only certain, sure knowledge can ensure a just government.
Plato’s Dualistic Solution
Therefore, in addition to the Sensible World, whose reality is constantly changing, Plato postulates the existence of another intangible and permanent reality: the Intelligible World. However, Plato was not the first philosopher to propose a dualism of knowledge. Parmenides came before him, stating there are only two methods: opinion and science. For Parmenides, Being is unique, eternal, and motionless. Plato applied the characteristics of Parmenides’ Being to his concept of the Intelligible World.
Accessing the Intelligible World
The Theory of Recollection and Eros
During his Socratic period, Plato transcribed his master’s teachings on the search for rational knowledge and universal definitions. In his transition period, Plato went beyond Socrates, proposing that we know universal concepts thanks to the soul. The soul is immortal and, before being embodied, it witnessed the permanent reality of essences (or Forms), which it forgot at birth. Thus, learning is a process of remembering (anamnesis), where sensible objects help us recall the Ideas they imitate.
The concept of Eros, or the desire for beauty, also drives us toward this higher knowledge. This journey happens in stages: from the beauty of a single body, to the beauty of actions, to beautiful thoughts, and finally to the Idea of Beauty itself. The Idea of Beauty can arouse all other Ideas.
The Divided Line and the Allegory of the Cave
Plato illustrates that there are gradations between the most real and the least real. He asks us to imagine a line divided into two unequal sections. One section represents the Intelligible World, and the other represents the Sensible World.
- The Sensible World: This is the world of becoming, of things that do not exist by themselves, which we perceive through our senses. Knowledge of this world is called Opinion.
- The Intelligible World: This is the world of eternal and immutable realities (the Forms or Ideas), captured by reason. Knowledge of this world is true Knowledge or Science.
The relationship between these realms is like that of an original to a copy. The higher segments are the cause of the lower ones and represent a more real, more certain form of knowledge. How does one move from one segment to another? Plato explains this with the Allegory of the Cave.
The inside of the cave represents the sensible world, where humans live as prisoners, perceiving only images. These images—shadows, reflections, and copies of sensible objects—are the lowest degree of reality. The first step toward enlightenment is to break the chains, turn away from the shadow world, and cross a boundary wall into a hallway lit by a fire. This represents moving beyond appetites to the level of sensible objects.
To exit the cave is to ascend to the intelligible world. The prisoner is forced into the outside world, representing the realm of mathematical entities and concepts. Mathematics relies on hypotheses to reach conclusions, but these hypotheses are ultimately based on the Ideas. The myth continues as the liberated prisoner sees the stars and then the beings of the day, illuminated by the sun. Finally, he can look at the sun itself, which represents the Idea of the Good.
Just as sunlight allows us to see objects in the sensible world, the Idea of the Good illuminates and reveals the other Ideas. And just as the Sun produces seasons, life, and growth, the Idea of the Good organizes and gives reality to all other Ideas.
Challenges to the Theory of Forms
A problem arises from this theory. If the Ideas are defined as separate, unitary entities like the Being of Parmenides, how can we have knowledge of them and their interrelations? This presents two options: abandon the Theory of Ideas or redefine its features. In his dialogue Theaetetus, Plato studies the first option, while in The Sophist, he pursues the second.