Baldur's Gate 3

But… categories aren’t better?

They are easier to grasp. Your example of thinking about alignments as pairs of qualities is the proof for that. Again: there are 9 distinctive alignments. They absolutely shouldn't be broken into pairs of qualities, each analyzed separately as people do it.

For example, for me there's no such thing as Lawful + Good, where Law forces the character to do this, while Good - that. It's "Lawfulgood" and it's the expression of a struggle to be as close to archetypal paladin or warrior-saint as possible. Fight, fail, get up, fight again. Struggle.

This isn’t the forum for writing essays about the nature of self and of minds, and the capacity for change, so I’m not going to do that here.

Way I see it, if the discussion requires it, then it absolutely is. If the discussion can't be resolved because the arguments can't be brought up, then what's the point of even starting the discussion?

Is a change in action a change in nature, or a facet of complex circumstance?

No single action is enough to determine the nature of man.

Can nature change without a correlating change in action?

Yes. I can chain a person to a wall, pump enough chemicals into her bloodstream that it remakes her into a violent monster, or perform full frontal lobotomy (Jekyll & Hyde scenario) and leave her like that. It will be impossible for her to commit any action, but her nature will change radically.

But your alignment is an (incomplete and over-generalized) aspect of that, not the whole of it, nowhere close.

That's how alignments are described and were described since the beginning, yes. The idea that an alignment limits the actions and choices of a character is entirely wrong and stems from the lack of proper understanding of how they should be applied to a game.