Why does Plato, in his Republic, say it is impossible for professors of education to put knowledge in the soul which was not there before?
What connections exist between Plato’s “Allegory of the Cave” and the theory of Social Construction of Reality?
Plato's purpose in writing The Republic is to create a better world, a divine world. In Book VII, Plato concentrates on enlightenment (education) through a parable commonly referred to the "Allegory of the Caves."
That allegory begins with prisoners, who have been there since they were born, sitting in a dark cave. There is a fire behind them, but they are chained in such a way that they cannot move their heads. They cannot look to the right or to the left; instead they can only see what is directly in front of them. The fire behind them creates shadows, of course, so when people walk behind the prisoners (between them and the fire) all the prisoners can see are their shadows. When the people talk, their voices are only heard as echoes by the prisoners. To the prisoners, these semblances of reality (shadows and echoes) have become reality; and the glimpse of the sun they can barely see outside the mouth of the cave is nothing like the reality of the actual sun.
Once the prisoner manages to free himself (presumably there are many ways a man may break free to be enlightened), he painfully (after being held in chains since birth) begins to see what is real and discovers that what he thought was real were simply shadows and echoes--pictures of reality. Eventually he is strong enough to be able to look directly at the sun, a symbol of good (which are truth and knowledge for Plato). This former prisoner now understands that what he learned in the cave was an illusion.
Now the prisoner is compelled, almost against his will, to return to the cave in order to tell others what he knows to be true; however, he can no longer see in the darkness, and he looks and sounds ridiculous to the prisoners there, and they do not listen to him. The only way this teacher can teach them is by learning to see in the dark again.
Plato explains the meaning of this allegory to Glaucon and concludes that teachers ("professors of education") believe that we all have to be taught in order to know that we are living in darkness and that our perceptions of reality are not correct. Plato argues that everything we need in order to be enlightened is already inside us. He says:
if I am right, certain professors of education must be wrong when they say that they can put a knowledge into the soul which was not there before, like sight into blind eyes.... Whereas, our argument shows that the power and capacity of learning exists in the soul already; and that just as the eye was unable to turn from darkness to light without the whole body, so too the instrument of knowledge can only by the movement of the whole soul be turned from the world of becoming into that of being, and learn by degrees to endure the sight of being, and of the brightest and best of being, or in other words, of the good.
Plato believes that everything we need to achieve true enlightenment already exists within us; we simply have to work to discover it.
Of course, when he is talking about knowledge here, he is not talking about finite knowledge, such as facts and figures and data; instead he is talking about a kind of ethical or reasoned knowledge.
The Social Construction of Reality suggests that some things exist only because we (society) agree to their existence: they are only real or true because we believe they are. This includes things like money; institutions such as marriage and government; and ownership, such as property. These could be compared to the shadows and echoes of a fire-lit cave.