"Beauty is in the eye of the beholder."
"One man's terrorist is another man's freedom fighter."
These quotes raise the issue of relativism—the philosophical view that truth is relative to the person holding the particular view. According to relativism, "She believes that P" means "P is true for her"; and to say, "P is true" may be misleading insofar as it omits the reference to the person(s) holding the belief that P is true. Truth is just an affair of personal or cultural belief.
Beliefs differ of course, depending on personal differences, cultural differences, and so on. The fact of differences in belief or opinion is acknowledged by everyone in the debate. What distinguishes the relativist is the relativist's view that the fact of differences in belief is given decisive philosophic importance. In other words, it doesn't make sense to talk of truth except as the view of one side or other of the debate. In other words, there is no standard of truth, no ideal standard, no divine standard, no cosmic truth to which various views are more or less adequate. Opinion is all there is.
The non-relativist replies: just because people differ doesn't mean that one of them can't be wrong. When there is clearly a right answer to a particular question, we see that the fact of disagreement doesn't make any difference about what's true.
Relativism may be extended from judgments about what is true to judgments about what is beautiful or good. Thus there is no standard of beauty, just preferences; it would not make sense to say that one person's aesthetic judgments are more mature or better cultivated than someone else's. Beauty and goodness are not real; they are merely the projected correlates of preferences. Thus if we express a view about the moral horror of Nazism, a relativist may say, "Well, that's the belief of your culture. The Nazis felt otherwise." Note: as a statement of fact, the observation is indisputable. The relativist uses that observation of fact as though it humiliates the critique of Nazism.
Some criticize relativism for making rational disagreement impossible, since, according to relativism, there are no criteria to which one can appeal that are not merely relative to one's personality or culture. If we disagree, we can either tolerate the other (e.g., the Nazi's are free to do their thing—who are you to judge?!), or we can fight. However people do sometimes effectively criticize and persuade one another, and older and poorer ideas do sometimes eventually get changed. This also happens across cultural differences. It would seem that people's value intuitions have more in common than the relativist is prepared to acknowledge.
Nevertheless, it is important to explore how people may reasonably differ in their judgments about truth, beauty, and goodness. One need not embrace either relativism or a monolithic and static conception of truth, beauty, and goodness. To some extent one may posit convergence, as evolutionary progress gradually brings views closer and closer. To some extent, one may recognize differences that tend to endure; perhaps there are certain aspects of many-sidedness that are structural, deep, and are properly represented by differing perspectives on truth, beauty, and goodness. Insofar as these perspectives are intelligible to all, e.g., tendencies to emphasize certain values more than others, then the prospect for mutual comprehension and cooperation in seeking wisdom remains open. Insofar as such differences are thought to be incommensurable, the relativist is vindicated.
Please study the following two arguments and their summary analysis in order to grasp something about the critique of certain kinds of poetry in the Republic and in order to grasp something about the critique of a certain kind of ideal.
Premise 1. The state should prohibit the publication of any poetry that grossly violates the truth of divinity or tends to weaken human character.
Premise 2. Poetry that portrays divinities as committing murder, adultery, or other morally repulsive acts, or portrays heroes as flooded by cowardly emotion, is poetry that grossly violates the truth of divinity or tends to weaken human character.
Conclusion. Therefore, the state should prohibit the publication of any poetry that portrays divinities as committing murder, adultery, or other morally repulsive acts, or portrays heroes as flooded by cowardly emotion.
Summary analysis of argument #1. Although, according to the standards of logic, the conclusion does follow from the premises, premise 1 is false, a fatal flaw in the argumen
Premise 1. Plato held that there are eternal standards of excellence and that poetry should be in harmony with those standards.
Premise 2. Plato advocated censorship of the arts, a totalitarian betrayal of human liberty.
Therefore, claims to eternal standards of excellence are to be suspected of being totalitarian.
Summary analysis of argument #2. Both premises are correct, but the conclusion does not follow. Therefore, the argument is invalid. (Note: in logic, validity and invalidity are properties of arguments, not of individual propositions, which may be true or false.)