Plato was greatly influenced by Socrates in formulating his moral philosophy or ethics. Like Socrates he said that there is a Good which is universal and independent of any particular culture. And there is a consonantal movement of thought from Plato's theory of Forms to his theory of moral philosophy. In his moral theory, he censured the Sophists' cultural relativism saying that the true nature of definition of justice is not related to a particular culture or society. If we want to have a clear vision of the justice, we have to make a universal Idea of good, says Plato. He argues that we can be deceived in the field of moral choice as we were deceived in the cave if we make judgments after experiencing particular cultures. Plato brought forth the Socratic notion that knowledge is virtue.
Plato invented two ways to express his ethics:
(1) The concept of the soul
(2) The theory of virtue as the fulfillment of functions
Plato's Concept of the soul:
Plato assumed that soul is the principle of life and movement. The body by itself is inanimate and therefore when it moves it must be moved by the principle of life, by soul. Plato described the soul as having three parts called reason, spirit and appetite.
Firstly, there is an awareness of a goal or a value and this is the act of reason; secondly, there is the desire toward action; the spirit which is neutral at first but responds to the direction of reason. Last, there is the desire for the things of the body, the appetite. Plato has summed that these three parts are linked together and must work together to achieve their goals. According to Plato, all the three parts have their goals, but the passion or appetite in goal seeking is incapable of distinguishing between objects that provide long lasting pleasure and those that provide pleasure for the short time.
Plato believed that moral evil is the result of ignorance .Evil or vice is inherent in soul when it is created. The soul has two parts namely rational and irrational. The rational past is created by the Demiurge whereas the irrational part is created by the heavenly gods. There is another cause of the disorder as when the soul enters into the body, the body persuades the soul to create disorder by overthrowing the rulership of the reason.
In addition the body creates stimuli which make the reason go away from the right direction. Evil is also transferred through the transmigration of the soul. In the process of becoming moral, men must recover his best inner harmony with which he has acquainted in the world of Ideas. The reason must overthrow the rule of appetites. The reason must take the control over the irrational parts of the self and distinguish the false knowledge. According to Plato, no one does anything which will be harmful to him. But man should do what is actually good but not good only for himself.
Virtue as the fulfillment of function
The good life is the balanced life and the balance can be achieved when each part of the soul does its assigned function. Reason has a function and reason is good only when it acts clearly and correctly. At the same time, spirit has a function and so do the appetites and when these parts do their function properly then the balanced life is achieved. According to the Plato, there are four cardinal virtues. Three of these correspond to the three parts of the soul and the fourth is the unity of them.
When the appetites are kept within limits and avoid usurping on the other parts of the soul, this moderation in pleasures and desires lead to the virtue of temperance. And when it becomes trustworthy instead of aggressive and defensive then the virtue of courage is achieved. And when reason remains undisturbed it achieves the virtue of wisdom. The forth virtue is justice which means proportion and harmony within the soul. When all three parts perform their functions and co-operate with each other, then the justice is achieved.
By grounding morality on the various functions of the soul, Plato felt that he had overcome the skepticism and relativism. Virtues or the right conduct of life are action which flow from knowledge, knowledge of the tripartite soul, the Forms, and the Idea of the Good. Only the few have such knowledge and they should control the conduct of the other members of society.