This came up in discussing rules sets, and being able to prove that one is superior to another. The whole line on truth arose specifically so I could demonstrate how 1) we don't have it, and 2) it doesn't apply to individual tastes in any event.
Someone upthread said, "I may or may not be able to know an absolute truth (or be able to verify it), but there are a number of things that are true enough to get the job done and function in the world."
1) is a thing which I am willing to agree to
a priori. However, it should be noted that, as with scientific data precision =/= accuracy. It is quite possible to be accurate without being precise. Demonstrating accuracy, of course, encounters the same problems I began discussing relating to worldviews. For that matter, so does determining accuracy in the first place.
Nonetheless, I am willing to say that (for example) Piratecat's DMing skills are better than those I possessed during the first game I ran (and possibly better than my skills now), and that this is a true, if not objective, statement.
Within the context of the above,
2) is not something which can be stated as a matter of truth. It is, AFAICT, a matter of opinion. It is your opinion that there is no true method of deriving relative value, apart from the subjective tastes of individuals. That does not mean that relative value is not "real", and that individual tastes cannot themselves be graded according to a "real" standard.
Prior to the development of the philosophy of science, there was no successful means to probe the rules of the physical universe. Even the advent of the scientific method did not prevent flawed conclusions -- and flawed observations, for that matter -- from proliferating (and this is as serious a problem now as it ever was). Flawed observations and flawed conclusions do not, however, negate the value of the toolset.
Prior to the development of the philosophy of science, much of physical nature was thought to be subjective -- either subject to an anthropomorphic will of its own, or to the whim of deity. Yet much that was thought unmappable has turned out to be chartable after all, and we have a good map of the physical interactions of the universe as a result.
That we have no similar means to map valuation, at this time, does not mean that there is not a "real" standard of valuation to be mapped. Moreover, it does not mean that a toolset will never be discovered that can do so, with the same level of result as that of the scientific method. What that toolset would look like, obviously, we have no idea (or, if you do have an idea, and are able to develop it sufficiently, a Nobel Prize may be in your future).
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I believe that the topic comes up in relation to rpgs so often because rpgs offer something akin to a language for understanding the dilemmas involved. The campaign milieu is an analogue for a world or universe, and it obeys both known rules and unwritten rules (regardless of how close the GM attempts to cleave to the RAW). Because the position of the GM exists (even if taken over by all the players as a council, and even if the GM attempts to suppress it as best he can), the milieu has an underlying valuation that is "real" from the position of the rpg characters. Frex, if the GM believes slavery to be evil, slavery is evil within the game milieu, affecting alignment (if the game has such a system), and very likely being punished when engaged in by the PCs....again, whether the GM intends to punish the players or not.
Likewise, because the RPG has winning strategies, and some way of measuring PC success, there is again a real form of valuation within the system. These things combine to give rpg players the basic ideas of this particular area of philosophy, and a language in which to discuss them.
Games like D&D not only posit real valuations existing (alignment), but postulate a toolset to explore the same (detect alignment).
(This is obviously not unique to rpg players.)
This is similar to how fans of
Star Trek or
Doctor Who could do a doubletake when Kip Thorne "solved" the Grandfather Paradox by invoking alternate universes. Those fans not only had the language to understand what Thorne was saying, but they had also already seen the same "solution" more than once within the context of their favourite programme. Simply put, although the solution made the front covers of magazines, it had been telegraphed long ago by sf media.