Plato's Republic

In Plato's Republic, Socrates goes to great lengths to explain and differentiate between the ideas of opinion and knowledge. Throughout society, most common men are lovers of sights and sounds. "Lovers of sights and sounds like beautiful sounds, colors, shapes, and everything fashioned out of them, but their thought is unable to see and embrace the nature of the beautiful itself (Republic 476b)." The few who do recognize the beautiful itself are followers of the sight of truth, the philosophers.

Knowledge is based on what is, or truths. The only established truths are the forms. The forms represent true, eternal, unchanging, or facts. Knowledge stems from the idea of forms. One who has knowledge must understand the forms. Only a philosopher has this understanding, and therefore only a philosopher has knowledge.

Contrary to knowledge, ignorance is based on what is not, or untruths. Opinion represents all that remains, therefore opinion is both what is and what is not. The opinion represents all truths other than the eternal unchanging forms. Those who love merely sights and sounds cannot obtain knowledge, for they do not recognize the forms in the sights they see, but only the sights themselves. These lovers of sights and sounds instead have opinions.

A man may see beauty in a woman, but this idea is relative. Compared to another woman, she may not seem so beautiful. Over time, her beauty will fail with age. Unlike the woman, the form of beauty itself will always remain beautiful. The man's thought of the beautiful woman remains merely opinion, while the form of beauty itself represents true knowledge.

Socrates goes on to describe the powers. "Powers are a class of the things that are that enable us - or anything else for that matter - to do whatever we are capable of doing (477c)." He explains that knowledge is the power that allows us to know, while opinion is the power that allows us to opine. However, he states that knowledge is an infallible power while opinion is fallible (477e).

According to the divided line (509d Ð'- 511e), knowledge and opinion are contained in two separate worlds. The world of appearance represents opinion, while the world of thought represents knowledge. The senses construct the world of appearance. It represents imagination and belief, the elements of opinion. Images, art, poetry, religion, objects, and artifacts all fall within the realm of opinion. All of these are things perceived through the senses or believed true. However, all of these thoughts are relative, indefinite, and fallible, which renders them opinions rather than knowledge. Like the world of appearance, the ideal world of thought represents the two aspects of knowledge, thought and understanding. Contained in the domain of knowledge are thought, mathematics, ideas, justice, and truth. All of these features of knowledge are established unchanging, infallible truths. Unlike opinion, these concepts of knowledge are clearly non-relative.

The most highly regarded idea in the realm of knowledge is justice. When Socrates first begins discussing the notion of justice in Books I and II his companions confront him with a relativistic view of the subject. However, the definition derived for knowledge in Book V sheds a new light on the matter. With the new definition stating, among other things, that knowledge remains non-relative, it becomes apparent that justice too remains non-relative.

Early on in the discussions about justice, Socrates and his comrades develop the initial definition that justice consists of speaking the truth and repaying whatever debts one has incurred. However, Socrates quickly points out that if a man were to borrow a weapon from a friend, and later the friend asks for it back when he has gone insane, it would not be just at all for the man to return the weapon to his now insane friend (331a Ð'- 332d). The discussion goes on to conclude that justice "gives benefits to friends and does harm to enemies (332d)." Again, Socrates swiftly refutes this definition by stating that a man does not always know who are his real friends and enemies. Both of these ideas of justice display relativity and therefore they fail as definitions. A variety of situations can easily disprove any classification of justice displaying such relativity. Exceptions will always exist.

Glaucon and Adeimantus decide to take a different path in trying to understand justice. He develops three classes of goods: things desired only for their consequences, things desired for their own sake, and things desired both for their consequences