Cultural moral relativism refers to the perspective that values derive from preferences and cultural differences. In this view, the ideas of right and wrong are not absolute, but instead vary from person to person and culture to culture. This idea was embodied by the early philosopher Protagoras who said that "man is the measure of all things." Plato argued strongly against this view, proposing that values such as justice and right conduct were absolute and beyond the realm of subjective viewpoints.
One of Plato's first arguments against moral relativism is that it is logically unsound. Plato claims that moral relativism has no ethical or logical ground to stand on, since it refutes itself. If all values and standards are subjective and dependent on perspective, then anyone is free to adopt as his own perspective the idea that moral relativism is false. By this argument, Plato says that cultural moral relativism undercuts itself by allowing in its own logic the possibility that it is false. Practically speaking, if subjective reality and preference are all that exist, then by rejecting moral relativism, it ceases to exist as a reality.
Plato proposed a multi-layered existence. There is the world of sensory perception that everyone inhabits, which includes the physical realities of existence. Plato argued for a higher level of being that he understood as a world of forms, ideas or concepts. For Plato, this world was the primary day-to-day reality. Plato argued that conduct comes from a reference to this world of forms. By this argument, there is an eternal idea or form of each moral principle, such as justice, piety or truth. When humans take actions that are just or truthful, they are modeling their behavior on an eternal and unchanging concept that gives them guidance.
Evil as Ignorance
Plato provided examples to illustrate the belief of Socrates that no one is purposefully evil. According to Plato, evil is simply the result of ignorance. Plato believed that all people are attempting to do what they understand as good. When someone commits a crime, for example, it is because he has a warped internal sense of what is good and beneficial. Somehow, wrongdoers get the idea that their acts will lead to some greater good. Through this argument, Plato claimed that everyone accepts good and beneficial action to be the goal, and so this idea of the good is universal and not relative. Cultural differences arise out of different manifestations of the idea of the good.
Plato established a long-lived psychological model by what he referred to as the three parts of the soul. There is a rational and moral part of the soul that loves truth, justice and good. There is a spirited part of the soul that loves worldly achievement, riches and victory. And there is an appetitive part of the soul that craves food and carnal gratification. Plato argued that the rational part of the soul should rightly be in charge, as it is most in tune with moral value. However, the task of aligning all parts of the soul is not easy, and many people fall by the wayside, giving in to baser urges and impulses. So Plato claimed that morals have nothing to do with culture, they have to do with which part of one's soul is in charge.