@Helen8220
Thanks for setting this up!
Here’s a question I was thinking about last night - I have met a few non-binary people who I can’t tell what their ‘biological sex’ is. I don’t think it’s my business to ask about their medical history/genitalia. I am happy to use the pronouns they ask me to use.
There will obviously be people in their lives who know what biological sex characteristics they have - those involved in their medical treatment, sexual partners. There will also be certain authorities that have the information, given the law currently requires people’s biological sex to be registered (but one could dispute if that should be the case).
In terms of how that person moves through their everyday life - how people refer to them, what spaces they’re allowed into - what do you think should happen?
Let's first of all pick apart the two different concepts you are throwing together here.
Non-binary people are typically (but not always) people who have been born either unambiguously male or female, but who feel they do not fit society's ideas of women and men, or they believe they fit both equally.
A few of those who identify as non-binary may naturally look androgynous or seek cosmetic surgeries to match their ideal body, but will typically (but not always) still be obviously male or female.
However, you mention medical history in this context, which suggests that you are conflating those born unambiguously male or female who later identify as non-binary with the exceptionally rare individuals who are born with ambiguous genitalia.
These individuals belong to a group of patients variously called intersex people or people with Differences in Sex Development (DSDs). Both are umbrella terms for about 40 different conditions that always affect either male or female people.
They are not actually intersex in the sense of being hermaphrodites, that is functionally both male and female. Such creatures do exist in the animal world, but the human animal is not one of them.
Now to your question. You say "I can't tell". That is a matter of perception. And perception is of course subjective. We cannot base legislation and policies on people's perceptions because that differs from person to person. Some people are not at all perceptive, others exceptionally so. Have you heard of hypervigilance, for instance?
It's a survival instinct developed by survivors of violence which helps them identify potential predators. The most common form is that developed by female victims of male violence, who will recognise males as male even when others do not.
So, while you may not be able to tell what sex those individuals are, women who are hypervigilant most certainly will be.
Additionally, there's also empirical evidence from qualitative and quantitative studies showing that female people are better at recognising female faces than male people. So, we have evidence that there are both individual differences in perception based on personal history and general differences in perception based on our sex.
Moreover, pattern recognition is one of the first skills children learn. It's not just another survival skill, but a vital ability we need to successfully navigate our world. Children aged four can reliably tell male and female adults apart, and as you can see from what I said about hypervigilance, this isn't a skill we lose as we age but one that we depend on throughout life.
A good example to look at is age. Remember those signs everywhere you can buy alcohol? If you look under 25 we will ask for ID before you can buy alcohol.
But surely, once you are 18, you can legally buy alcohol. Why card anyone who looks under 25? Because perception does not always match material facts.
You may look 22, especially when dressed and styled accordingly, but only be 17. You may look 15 but actually be 19.
Normally that doesn't matter. But if you want to draw on the legal right to buy alcohol, perception means nothing. Only your actual age counts.