-[TODO: the function of saying "or purple" is to appeal to a principle of equality: if there were purple people, they would get covered by the universal rule. But, Amethyst really is an alien, which would be a different cluster]
+How is the old-school liberal to reply to this? The function of saying "or purple" is to appeal to a _principle_ of equal treatment. Adding a fantasy race in there highlights the universality of our commitment to equality: purple magical alien gem superheroines might not exist, but if they _did_, they would be entitled to the same rights and dignity as everyone.
+
+But how should our principle of majestic equality be applied? [Categories summarize information](https://www.lesswrong.com/posts/esRZaPXSHgWzyB2NL/where-to-draw-the-boundaries)—[cluster-structure in the real world](https://www.lesswrong.com/posts/WBw8dDkAWohFjWQSk/the-cluster-structure-of-thingspace). As a matter of AI design, there would be no _functional_ reason to assign entities to different categories, if they didn't differ in _some_ decision-relevant ways. The reason it's pretty weird to reference Amethyst's skin color in a lesson about human racism, is because the challenges Amethyst might face as a gem in a world of humans—perhaps the perceptual skew of living thousands of years when most humans don't see a hundred—is going to depend on the ways in which gems and humans are actually different.