Plato discusses theories of knowledge throughout his famous dialogue, the Theaetetus. He discusses many different ways of learning and attempts to define knowledge. Plato does this through a conversation between a few characters: Socrates, the famous philosopher; Theodorus, an aged friend and philosopher of Socrates; and Theaetetus, a young man who is introduced to Socrates before a discussion. One aspect of knowledge which they review is perception. It is defined and explained by Socrates, to the young and innocent Theaetetus. Perception is defined by Floyd H. Allport in his book, Theories of Perception and the Concept of Structure, as the way things look to us, or the way they sound, feel, taste, or smell. It is not the way things are exactly, but the way we see them; or because it involves all of the five senses, the way we perceive them.
Perception is not restricted to sight only, the world has countless numbers of sounds, smells, and textures. Perception is the way things look to us because even though something might seem to be one way, it is another. For example, the Muller-Lyer illusion makes people see wo lines of different lengths, while the lines are the same size. This illustrates the fact that just because you perceive something to be a certain way does not mean that it is true. Truth and perception do not necessarily coincide.
This is also true with belief. When seeing something that is too far fetched to be real, then you find it hard to believe. Perception is merely an experience [which] is just a stage along the causal process leading to belief. Perception is not truth or belief, but it is an important (however, not ecessary) step to reaching them. In Platos Theaetetus, the three characters in the conversation have a discussion on perception and how it relates to the world. Plato recounts Socrates telling the young Theaetetus how, contrary to his belief, perception is not knowledge. Perception is too varied, Socrates says. He gives the example of a breeze blowing; one man can be made cold from the wind, while the man next to him might not be cold at all. The blowing wind is the same temperature, but as defined above, perception is the way things look to us.
Everybody is different and so everybody will therefore experience the world in a different way. This is what Socrates explains to Theaetetus, who sparked the topic of conversation with his reply, knowledge is simply perception. He was incorrect in his thinking because knowledge consists of justification, belief, and truth. Since two of these aspects are unattainable with perception alone, then perception can, in no way, be considered knowledge. Theaetetus quickly learns the error he has made and the dialogue and the examination of knowledge continues.