What did Plato mean by the divided line?
Below the rulers are a guardian class of police and soldiers, who correspond to the spirited part of an individual soul, and at the bottom are the mechanics, servants and farmers, who are like the appetites, or an individual’s physical body.
To ensure that the rulers love and serve their city above all else, Plato suggests that the family be abolished. In his social structure, men and women do not have to base their lives on their biological reproductive roles. Private property is unnecessary, too, as are monogamous sexual relationships or traditional marriage. The smartest, healthiest, and altogether best boys and girls will be specially trained, beginning with a simple diet, plain living conditions, and exercise in the open air.
Because the poets lie and teach impiety, there will be no literature in the new curriculum. In young adulthood, the young rulers will be taught mathematics and philosophy. At the age of 35, they will be sent out into the world for 15 years to serve the community as lower administrators, police, and soldiers. At the age of 50, they will be ready to rule, all the more so because it will be against their desire to devote the rest of their lives to study of the forms. (Plato, like many since him, believed that those who do not wish to rule are the very ones who should rule.)
What Plato meant by the divided line is explained by Socrates in the Republic:
Now take a line which has been cut into two unequal parts and divide each of them again in the same proportion, and suppose the two main divisions to answer, one to the visible and the other to the intelligible, and then compare the subdivisions in respect of their clearness and want of clearness, and you will find that the first section in the sphere of the visible consists of images. And by images I mean, in the first place, shadows, and in the second place, reflections in water and in solid, smooth and polished bodies and the like: Do you understand?
What Socrates hoped his listeners would understand was that what they saw through sight was less clear and further from the truth than what they were able to “see” in their “mind’s eye” or understanding.