+Defining sex in terms of gamete size or genitals or chromosomes is like the using the never-flipped first bit in our abstract example about the world of length-20 bitstrings. It's not that people _directly_ care about gametes or chromosomes or even gentials in most everyday situations. (You're probably not directly trying to mate with most of the people you meet in everyday situations, and sex chromosomes weren't discovered until the _20th_ century.) It's that that these are _discrete_ features that are [causally](https://www.lesswrong.com/posts/vhp2sW6iBhNJwqcwP/blood-is-thicker-than-water) entangled with everything _else_ that differs between females and males—including many [correlated](https://www.lesswrong.com/posts/cu7YY7WdgJBs3DpmJ/the-univariate-fallacy-1) statistical differences of various [effect sizes](/2019/Sep/does-general-intelligence-deflate-standardized-effect-sizes-of-cognitive-sex-differences/), and differences that are harder to articulate or measure, and differences that haven't even been discovered yet (as gametes and chromosomes hadn't respectively been discovered yet in the 16th and 19th centuries) but can be theorized to exist because _sex_ is a very robust abstraction that you need in order to understand the design of evolved biological creatures.
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+Discrete features make for better word _definitions_ than high-dimensional statistical regularities, even if most of the everyday inferential utility of _using_ the word comes from the high-dimensional statistical correlates. A dictionary definition is just a helpful pointer to help people pick out "the same" [natural abstraction](https://www.lesswrong.com/posts/cy3BhHrGinZCp3LXE/testing-the-natural-abstraction-hypothesis-project-intro) in their _own_ world-model.
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+(Gamete size is a particularly good definition for the natural category of _sex_ because the concept of [anisogamy](https://en.wikipedia.org/wiki/Anisogamy) generalizes across species that have different sex determination systems and sexual anatomy. In birds, [the presence or absence of a _W_ chromosome determines whether an animal is _female_](https://en.wikipedia.org/wiki/ZW_sex-determination_system), in contrast to [the _Y_ chromosome's determination of maleness in mammals](https://en.wikipedia.org/wiki/XY_sex-determination_system), and some reptiles' sex is determined by [the temperature of an lain egg while it develops](https://en.wikipedia.org/wiki/Temperature-dependent_sex_determination) (!). And let's not get started on the [cloaca](https://en.wikipedia.org/wiki/Cloaca).)
+
+But because our brains are good at using sex-category words to simultaneously encode predictions about _both_ absolute discrete differences and high-dimensional statistical regularities of various effect sizes, without our being consciously aware of the cognitive work being done, it's easy to get confused by verbal gymnastics if you don't know the theory.
+
+I sometimes regret that so many of my attempts to talk about trans issues end up focusing on psychological sex differences. I guess I'm used to it now, but at first, this was a very weird position for me to be in! (For a long time, I [really didn't want to believe in psychological sex differences](/2021/May/sexual-dimorphism-in-the-sequences-in-relation-to-my-gender-problems/#antisexism).) But it keeps happening because it's a natural thing to _disagree_ about: the anatomy of pre-op trans women is not really in _dispute_, so the sex realist's contextual reply to "Why do you care what genitals someone might or might not have under their clothes?" often ends up appealing to some psychological dimension or another, to which the trans advocate [can counterreply](https://thingofthings.wordpress.com/2018/06/18/man-should-allocate-some-more-categories/), "Oh, you want to define gender based on psychology, then? But then the logic of your position forces you to conclude that butch lesbians aren't women! _Reductio ad absurdum!_"
+
+This is a severe misreading of the sex-realist position. No one wants to _define_ "gender" based on psychology. Mostly, definitions aren't the kind of thing you should have preferences about: you can't coerce reality into changing by choosing different definitions! Rather, there's _already_ a multivariate distribution of bodies and minds in the world, and good definition choices help us coordinate the concepts in different people's heads into a _shared_ map of that territory.
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+_One_ of the _many_ distinctions people sometimes want to make when thinking about the multivariate distribution of bodies and minds in the world, is that between the sexes. But sex is by no means the only way in which people differ! In many situations, you might want to categorize or describe people in many different ways, some more or less discrete _versus_ categorical, or high- _versus_ low-dimensional: age or race or religion or subculture or social class or intelligence or agreeableness.
+
+It's possible that the categories that are salient in a particular culture ought to be revised in order to fit the world better: maybe we _should_ talk about categories like "masculine people" (including both typical men, and butch lesbians) more often! But the typical trans advocate shell game of just replacing "sex" with "gender" and letting people choose their "gender" isn't going to fly, because sex actually exists and we have a need for language to talk about it—or maybe, the fact that we have a need for language to talk about it (the fact that the information we observe admits compression) is what it means for sex to "actually" "exist".
+
+If trans advocates go astray in disbelieving that
+
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+gamete size or genitals or chromosomes someone has,