No, the world does not need another alignment thread, but I want to drill down on a specific point. I apologize in advance.
Compared to past editions, 5e alignment definitions are a lot less clear, almost to the point of being flavor text. So I can understand those who see no use for them. I think alignment can be very useful for worldbuilding and NPC design, but that requires useful, believable definitions. I wouldn't say even past editions have been great at this. So here's a shot at clear, understandable alignment definitions that I think most people might buy as plausible, but I'll settle for useable in-game. I'm certainly NOT proposing this as the "right way to do alignment". I do hope it provides some help in thinking through the issue.
My base assumptions are that alignment should be 1) intuitive (i.e. believable), and 2) Good/Evil and Law/Chaos are in opposition. I think Good/Evil works but Law/Chaos as usually framed does not. Chaos is the problem.
Most people seem to agree that Good is a Golder Rule type philosophy (do unto others...). I frame this as agency: a Good person acknowledges the agency of others and an Evil person does not. If someone believes something different than me, I might find them misguided, but they still have that right to belief. This definition satisfies both my assumptions.
But an intuitive definition for Law usually is "obeys the law" or "respects the law". These seem intuitive, but their opposites do not unless we want insane Chaotic characters, which some past editions encouraged. "Disrespects the law" is almost OK for Chaos, but what does that mean in practice? I still think you end up with "LOL I'll do want I want" as a justifiable interpretation.
Part of the problem is that in OD&D, we had Law and Chaos, which basically meant Lawful Good and Chaotic Evil. For some reason, we understand how to disentangle Law from Good (authoritarian regimes as Lawful Evil), but separating Chaos from Evil is harder. I think the reason is that, in real life, there aren't any "real" Chaotic societies (I'll explain below). But since the 1st Edition of the Monster Manual, elves have been canonically Chaotic Good. That's a rather important group of demi-humans to not fully understand their default alignment!
So to get a useable definition of Chaos, we also need to refine Law as a subtle reworking of the "respect" concept. I propose the following:
A Lawful person accepts the legitimacy of law that is external to themselves; a Chaotic person does not.
This definition is close to respect, but slightly different. It says that one can recognize the legitimacy of a body coming together to determine their laws, whether or not you agree with the outcome. For example, I'm sure we can all think of countries whose laws we do not admire. But do you then think those countries and their laws are illegitimate? I imagine there could be a few of these, but in general, we let sovereign countries be sovereign and run their internal affairs. In other words, we follow the Rule of Law as it's known in political science. So a Lawful person follows their own country's laws, even if some of them seem unjust. That same Lawful person would express disapproval of another country's laws by not traveling there or by biting their tongue.
By the way, it's a Neutral Good person who would more loudly complain and protest about unjust laws, because by not being Lawful they are more comfortable saying some laws are illegitimate.
So what does it mean for a Chaotic person to not view "external" laws as legitimate? Simple--only their own internal laws are legitimate, their "code". A Chaotic Good person understands that others have their own codes and they are legitimate for them. A Chaotic Neutral person values their code above all, and is not concerned whether or not it infringes on the agency of others. Note that this definition allows the Chaotic Neutral to not be a lunatic! They could even fit into a Lawful society, never respecting it but discretely carrying out their code whenever possible. Finally, I think this definition gets us very close to the tradition definition of Chaotic Evil: a person who respects neither agency nor the legitimacy of any law. In all these cases, I don't think any of these Chaos alignments correspond to any real human society. Our definition of "society" presupposes a minimum level of Law.
I came to this definition precisely to answer the elf Chaotic Good question: what sort of society could this be? I decided that elves are mostly bound together by heritage and a deep abiding for one another, but following any cause is always a matter of individual persuasion that can be withdrawn at will. Thus, elves need leaders good at individual persuasion, which comes down to raw charisma and magnetism. Essentially, this makes elfish society a "charismatic democracy", where elves rally around causes they believe in, following leaders charismatic enough to hold the cause's believers together. This is very different from any human society I've even of, with the possible exception of very small groups bound by some affinity; communes and cults come to mind.
I think these definitions get close to the intentions of many historical iterations of alignment in D&D, but are less ambiguous and therefore more able to be put into practice in a game setting.
