[Thought experiment] If alignments are objective how do we know what they represent?

[OldTrees1]

All "moral" means, by your own statement, OldTrees, is "what one ought to do." I assume - and correct me if I am wrong - that there is a hidden component that prevents conflating "you ought to maintain your car so that it doesn't break down" with more traditional conceptions of morality.

The lack of a qualifier is the "hidden component". Morality is the end onto itself in contrast to instrumental ends (maintain your car so that it doesn't break down). It is not "What ought one do in order to X?", rather it is just "What ought one do?".

But for objective morality, this would be a mistake. If your ideals align with a non-good alignment, then you ought to live by that alignment.

You keep using the phrase "objective morality" to mean something other than its definition. https://en.wikipedia.org/wiki/Moral_universalism I give up. I have provided links. I have explained it a few times in a few ways. IRL this week is going to be too stressful for me to continue this exercise. So I am bowing out. Thank you for humoring me for this long. While there was a failed communication, it was very respectful discussion.

Right, and this implies that if a fictional setting postulates an objective moral reality internally that means that while there may be multiple moral theories held in-universe, one of them is correct and all the others are wrong.

Generally I would say that fantasy comes at this from a religious, rather than philosophical question. Specifically most fantasy settings aren't 'all myths are true' they're 'this specific myth is true' and that specific myth usually includes a deity/deities who determine the moral system that governs the setting.

As a result, the question of what alignments represent, in a particular universe, is what the gods say they represent, and questioning the gods is pointless because the gods make the decisions and there's nothing a mortal living in such a setting can do about it.

I think a lot of players find this weird, in part because the kind of deity-derived moral certainty implied works better for a monotheistic system with a distant and presumably all-powerful creator entity rather than a polytheistic system where a bunch of gods squabble amongst themselves. This is why various writers working in FR felt obligated to create a level above the gods in the form of Lord Ao because the idea of FR deities, as presented, mediating an moral system at all was laughable. This is also probably why a huge amount of modern fantasy has retreated from polytheistic systems and back toward distant monotheistic non-interventionist creator deities. One god = one truth is simply a much simpler equation for addressing ethical questions when worldbuilding.

Sorry but my gut reaction to Divine Command theory is Socrates' dialogue Euthyphro. If the gods (or powers) dictate the definition of the alignments, then there is a very good argument for the alignments not being morally relevant. I won't go further than reference it here due to forum limitations.

My second reaction is you mentioning the laughable squabbling. I have a headcanon that the shape the cosmology depends on which alignment created the universe (since Aboleths once predated this universe). Obviously the Great Wheel was created under Lawful dominance.

Personally when I do use an objective morality I do it independent of the gods. It is just a fact of that reality.