The theory rests in the myth that describes people chained within a cave. The only images they see are the shadows of objects and animals held in front of a fire that is behind them that reflects on the cave walls in front of them. That is all they had ever seen so that is what they believe to be real. One day a man escaped the cave and went outside. With the sun he saw what was real in the world and realized all he ever saw were just shadows. He went back to the men in the cave and told them all this. He told them that they too could see the outside if they broke free of their chains but they didn't believe him.
The environment of the cave to Plato symbolizes the physical world of appearances. Escaping into the sun-filled world means the transition into the real world that is full and perfect. A world where things are not viewed only in a material sense. It is here that the whole of Plato's philosophy is summed up. Plato's theory of knowledge is devoted to definitions of science and knowledge. Developing the argument from the lower consciousness to the higher consciousness, in which perception, opinion, reasoning are closely examined.
Cornford F.M in his interpretations "Plato's Theory of Knowledge", the phrase "degrees of reality" is found in many commentaries to describe the aforementioned hierarchy. Vlastos' "A Metaphysical Paradox" and "Degrees of Reality in Plato." Cornford describes this as "a distinct order of realities."
Plato's ethical theory rests on the assumption that virtue is knowledge and can be taught, which has to be understood in terms of his theory of Forms. One of his famous arguments is that to "know the good is to do the good". Being the world of forms, which is the proper object of knowledge.
Of interest to our discussion is his later work that features Socrates and his pupil theaetetus in a dialogue named after the latter.
Theaetetus is introduced to us as a valiant and a hero of the battle of Corinth and of the dialogue. He is a disciple of Theodorus, a reputed geometrician, whose specialization is thus indicated to be the propaedeutic to philosophy. Theaetetus is introduced as wounded and also as having several similarities with Socrates, same contrast sharp mind and the unattractive features. Theodorus presents the younger man as courageous, intelligent and selfless. These qualities are seen as dialogue heats up.. Socrates is impressed by these credentials and invites theaetetus in a witty discussion on different issues. After overcoming the initial sense of wonder, he rises to the occasion, and begins to follow the flow of the discussion eventually he's able to comprehend the consequences of his own answers. The question about the "nature of knowledge" opens his mind and encourages him to think not only in a mathematical sense which he is used to but also in metaphysical sense. Eventually it dawns on him that "there are universal conceptions of being, likeness, sameness, number, which the mind contemplates in her."
In the dialogues Plato devotes himself to coining definitions of knowledge, conception, science and the like but at the same time tearing down the same definitions in an attempt to invoke in the mind of the student a desperation that will cause critical thinking. In the first part when asked his opinion