Ever since its discovery in 1930 astronomers have debated over whether or not Pluto deserves to be classified as a planet. With the recent discovery of Xena, and other large Kuiper Belt objects, this question has taken on a new perspective. Well, in the news this week are stories that tell us that the International Astronomical Union, in a less than unanimous vote, has just stripped Pluto of its designation as a planet. It would seem that "planet" is in the eye of the beholder; it all depends on your criteria and astronomical perspective. It's not as cut-and-dried a thing as a star or black hole.
I seem to have the habit of making abstract connections, and this topic suggests the issue of moral relativism to me. You see, many persons in our modern culture have the view that morality — right and wrong, good and evil — is simply a matter of personal or cultural definition. For this reason, claiming that something is "good" merely implies that it conforms to some humanly constructed definition of what passes for good versus bad. And the criteria can change over time. So, just as the new definition of a planet no longer includes Pluto, so can moral standards change to include or exclude certain behaviors. Slavery can be acceptable in certain times and cultures, but repulsive in others. Homosexuality can once be considered deviant behavior, but then come to be celebrated.
This view of morality would seem to be the necessary one in a purely material world, i.e., one without God or any metaphysical structure that pervades our minds. Without the ability to appeal to the supernatural, moral sensibilities must simply emerge from the will, emotion, and reason of human creatures. And since humans are individuals and change over time (even "evolve" according to present naturalistic theory), then morality may be expected to change as well.
To theists, this seems a fairly obvious truth. To have an objective, unchanging standard you have to have a mind external to your own which can impose it upon you. And it is a meaningless imposition unless there is reason and consequence for compliance with that standard. However, it is common for atheists to object to this conclusion. They often do so in one of two ways.
1) They misunderstand us to be implying that they are immoral people. But this is not at all what we are saying. Since we believe that the moral law is incumbent upon every human, and is woven into the very fabric of our souls, we are not at all surprised to find even atheists dancing to its tune (to mix my metaphors). The fact that atheists very much want to be thought of as good people is only a tacit admission that they understand that there is such a thing as "good" and that it is good to be good. But if morality is merely a human convention, then the most that an atheist can be claiming is that they are morally fashionable.
2) They are quick to point out their own moral concerns and offer their own ethical systems, but these are simply not a response to the point. There is a difference between having moral sensibilities and grounding them as objective. If your moral ideas originate from your own mind or the consensus of your community, then you have not grounded them upon any fixed standard. And if there is no objective standard upon which to base morality, then you can never say that your system is closer to that standard than some other or that you have improved it from one generation to the next. All that you can say is that one ethical system is "different" from another, and that you happen to like your own. To say that your system is "better" than another is a tautology; you are simply saying that your moral expressions conform more closely to your own system than does theirs.
Not everyone in the International Astronomical Union was agreed to remove Pluto's planetary status. Are planets just celestial objects as defined in a particular way and these dissenting astronomers took issue with that particular definition, or are planets particular things and the astronomers were simply divided over the facts that would go into placing Pluto in one category or another? It is a question that mirrors our modern moral debate. But there is at least one way in which this analogy fails: These astronomers were involved in a debate over an understanding of real objects, which they all believed in and that do not go in or out of existence depending upon the results of a vote. The moral realist may not always order his steps well, but at least he is dancing with real angels and demons. The relativist, on the other hand, is simply dancing with his own shadow.