this is a point i was working towards earlier when pointing out that biological sex is a spectrum and not binary. sex is basically the physical characteristics and traits, whereas gender is a social construct built on top of that regarding societal expectations, how they're expected to present themselves, and other stuff, and everyone gets assigned as being "male" or "female" depending on where they fall on the sex spectrum (or "intersex" if its too ambiguous to fit in either one). whats in somebody's pants, their sex, is irrelevant, unless we're gonna insist on checking everyone's genitals all the time; their gender, what they present themselves as socially, is the part thats relevant to others.
why does it only need to be male or female though? sex isnt binary, so whats with the insistence on shoehorning everyone into 2 categories, other than tradition, homophobia, and fragile masculinity?
I get that that's how you, and probably a lot of people define the words sex and gender, and how they differ from each other. And that's fine, ultimately I think it's more important that people are clear on what other people mean than the specifics of what words are used. Which is why generally if I'm talking to people who use those words that way, I'll try to use them that way too. And I can see how having that distinction would have advantages in discussing transgender issues. And really, that's probably the primary reason that personally, my default is to not draw any real distinction between them. It's extremely uncommon that I'm in a situation, especially in real life, where there'd be any point to having a different definition for the words sex and gender. I think most people, most people who don't really have any connection to or reason to frequently discuss anything to do with transgender issues that is, don't really think about it enough to really have different definitions for both words. If you do, then it makes sense that you'd want words to clarify what you're talking about. But if your life almost never warrants a distinction, and like a lot of people mine doesn't, it doesn't make sense to have two meanings if the words are almost never actually used intending that level of specificity.
I'm not a grammar nazi, I'm generally not one to change how I use words just because "the dictionary says so". But for the same reason neither do I care much what words are used so long as the meanings are clear in the context.
So, I try to keep in mind the difference amongst audiences that are likely to be paying attention to the difference, but virtually never do otherwise.
As for "why does it only need to be male or female" or "why shoehorn people into those categories". Well, I suppose it doesn't need too. But in my real life, it's probably almost never that I've encountered a need for a third category. If one day I do, I suppose I'd try to respect that.
But, with how my mind works mentally, on a purely instinctive level aside, I'm not sure my brain has any categories except male and female. I've never met someone where my brain hasn't mentally labeled them as one or the other.
But hey, that's just my brain. There's no need for society to follow that legally. Nor do I have to follow it in terms of how people wish to be addressed. And I see no reason why I should do so if doing so would be disrespectful to someone. There's just no need to be rude or disrespectful to people who are asking for so little. And really, I don't think someone who identifies as a particular gender, and asks that people address them as such, as asking for very much at all.
And on the subject of how my mind intrinsically categorizes people. ANT asked what qualifies as "sounds like a female, looks like a female, acts like a female" actually means.
As far as my mental classifications go, which at the time I was arguing that everyone's own mental classification can function as a way to identify gender without relying on chromosomes. That's the thing, I'm don't think it has to be explained. Our brains have evolved to do a great job identifying people as male or female without knowing things like chromosomes.
We've evolved an amazing ability to instantly identify men and women apart based on barely more than a glance, or half a second of hearing someone's voice. Our pattern recognition for it is phenomenal.
![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
in Japanese culture. 
