On March 10th, campaigner Christie Elan-Cane lost an case in the Court of Appeal against the UK government's policy that the "Sex" field on the British passport can only contain "M" or "F". The case sought the provision for a third "X" marker to be recognised in passports. This was an appeal against the original decision by the High Court in June 2018, and Elan-Cane has indicated that her legal team will seek permission to appeal the new decision so that the case may be head in the Supreme Court.

Several countries have already introduced laws which introduce a recognition of nonbinary markers on identity documents, while others have avoided the issue by removing gender & sex from their identity documents.

Elan-Cane argued in the case (link to original High Court judgment), that the government's policy violated the right to a private life, which is guaranteed by article 8 of the ECHR, of which the UK is currently a signatory. This argument was rejected by the court, but I'm interested in a wider view:

What other arguments, both legal & moral, have been used on both sides of this debate internationally? Is there a need for this information to be included at all? Clearly some countries get by without including a "Sex" field on their passports at all.

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    Are the comments from the court not sufficient? That at the moment there is no broad concensus and just because this campaigner wants X doesn't mean anyone else does. Related to New York's recognition of 31 Genders
    – Jontia
    Mar 11, 2020 at 9:59
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    @Jontia Just to clarify for others, New York does not recognize 31 genders: they have 3 options for gender (M, F and X). As the link you provided shows, the "31 genders" is actually just a list of 31 gender related terms that one might want to be aware of as part of "Courtesy 101"
    – divibisan
    Mar 11, 2020 at 15:43
  • This question is a candidate for gender-neutrality. However, with five tags already, I will leave it to you decide whether to re-tag the question.
    – Rick Smith
    Apr 8, 2022 at 16:20

1 Answer 1


Note: This answer discusses including biological sex on an official ID card (like a passport). This answer does not discuss including gender. I feel that a good discussion about including gender would require establishing what gender is in a universally acceptable way, which would be a large topic in itself. (Also perhaps a separate topic, as some folks might argue that biological sex and gender should both be listed in separate fields.)

tl;dr The primary argument for including biological sex is that it's immutably associated with a person and relatively easy to recognize/verify. The primary argument against including biological sex is that some people feel offended by it, e.g. due to feeling that it violates their privacy or ability to self-determine.

Background: Biological sex is a subset of genetic profile.

Biological sex is essentially about if a person consistently expresses the genetic content associated with Y-chromosomes in their cells.(Note 1) To simplify, it's basically saying if someone has a Y-chromosome.

Unlike most of a person's DNA profile, biological sex is highly observable.(Note 2)

Main point: It's about whether noting biological sex is more useful than objectionable.

The main argument for including biological sex is that it's useful in verifying identity.

This has two common applications:

  1. Defense against fraud.
    This is part of a defense-in-depth strategy in that, while checking someone's biological sex is by itself insufficient to establish the legitimacy of their claim to an identity (e.g., as the rightful holder of a passport), it's still a major filter for little effort.

  2. Identifying someone in a search.
    If you're looking for someone, it's helpful to know their observables: stuff like height, weight, sex, race, age, hair color/style, what they're wearing, etc., can be useful. Observables are more helpful when they're more immutable and more easily observed.

I suspect that most reasonable people can agree that biological sex is useful for the above reasons; so, those who want to exclude it probably have specific objections to it beyond concerns about its utility.

I've anecdotally noticed two different types of objections to biological sex being included:

  1. Biological sex is private information.
    While biological sex is highly observable by default, some folks wish to modify their apparent sex. Having their actual biological sex noted on an official document undermines their intent.(Note 3)

  2. Biological sex is offensive.
    Some folks feel that biological sex is an inherently offensive concept. Common reasons seem to include a belief in personal control over gender identity and disdain for biological determinism (discussed in a "Tangential" section below).

Most folks don't consider biological sex to be private information. In fact, I'd guess that, among the observables typically given on an ID card, it's more common for people to feel uneasy about the fields for age, weight, or a potentially unflattering photo.

Likewise, I'd guess that most folks don't find biological sex to be offensive. However, biological sex can be seen as undermining the interests of trans-gender/sexual individuals,(Note 4) potentially even exposing them to increased risk of hate crimes.

Conclusion: It's about if utility is greater than objections.

I think that most reasonable people would agree that having biological sex on official identification cards, like passports, can have its uses. So, those who argue against its inclusion likely do so because they consider biological sex to be private information or offensive.

Tangential: Regarding disdain for biological determinism.

Some folks are free-will compatibilists. Even if you show them a machine that can predict their future decisions,(Note 5) they'd still feel like they had decision-making power.

By contrast, some folks are free-will incompatibilists. If you showed them a machine that can predict their future decisions, then they'd feel like they lack the power to make such decisions freely. They'd probably hate the machine for one of two reasons:

  1. They'd feel that the machine is stealing their free will from them.

  2. They'd feel that the machine reveals that they never had free will in the first place.

Biological determinism is similar. Compatibilists may feel comfortable with the concept of genetics determining their nature, while incompatibilists may feel it to be utterly dehumanizing.

Personally, I'm a compatibilist, so I think biological sex is a cool concept; that it's so powerful in its predictive ability makes it awesome. But for incompatibilists, biological sex may feel violating; like it robs them of their power to be a free person.

I note this because some folks don't like the idea that they have a biological sex that says anything meaningful about them. Assertions to the contrary can come across as an existential attack against their personhood.

Tangential: Binary sex is probably too limiting though.

Almost every scientific theory about anything is wrong. It's probably a safe bet that even our best theories of physics are somehow wrong; just, at any point in history, we're not quite sure how/why yet.

Biological sex is no exception: we know it to be an imperfect concept. This doesn't mean we should ditch it because

All models are wrong but some are useful

Famous quote from George E. P. Box

, and biological sex is definitely a useful model.

That said, we shouldn't use a model when it doesn't work. And there're cases in which the male/female dichotomy doesn't fit, e.g. for intersex or transsexual individuals.

My point here isn't about political correctness nor about gender identity. Instead, what I'm saying is that when a person isn't objectively well-described as either male or female, forcing an ID card to say one or the other is simply printing misinformation. And that's an objectively bad thing to do.


  1. Most biological females have XX chromosomes while most biological males have XY chromosomes. However, there're rare conditions which deviate from this norm; for example, ~0.075% of males are XXY, and ~0.005% of males are XX. The exact wording used in the above answer was selected to avoid misclassifications that can arise from assuming the basic XX/XY dichotomy.

  2. More precisely, it's easier to connect external observables to statements about a person's DNA. By which I mean, a lot of consequences of a person's DNA can be highly observable, but the implications of many observables aren't trivially mappable to a DNA profile, making it more difficult to appreciate such associations.

  3. One common argument for modifying apparent sex is to advertise gender. This answer is intentionally avoiding discussing gender – that'd require covering a lot more ground first, and this answer's long enough already.

  4. This answer discusses "biological sex" as a function of genetics, not external appearance, such that a transsexual's ID card would include their physically apparent sex at birth (rather than post-transition). This isn't meant to imply anything about the nature of transsexuality nor transexuals; it's just the specific definition of "biological sex" being discussed; discussing alternatives would require extending this already-very-long answer.

  5. Such a decision-predicting machine is often described in at least three contexts:

    1. as a hypothetical in such philosophical thought experiments;

    2. with respect to machine-learning algorithms predicting folks' behaviors based on, e.g., their social media interactions;

    3. whenever people feel like they're being predictable.

    I note this to help ground the concept in everyday experience, to show that it's not just some esoteric philosophical concept. For example, have you ever met someone who feels like they're not "truly alive" if someone else can guess what they'd do? Like being predictable demeans their humanity, making them less of a person? That's incompatibilism!

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    Didn't get to a lot above. For example, passports with a biological sex that doesn't match apparent sex may be problematic for travelers visiting areas where homosexuality, etc., are illegal or/and openly hated. Still, feels like the above answer got pretty long already.
    – Nat
    Mar 12, 2020 at 7:31
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    You've written a lot about biology and determinism, but gender is very much the question; plenty of countries already issue transgender people with the correct changed passports.
    – pjc50
    Mar 12, 2020 at 8:24
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    @pjc50: The question asks about both sex and gender. I'm comfortable writing about sex as it's a largely scientific topic.
    – Nat
    Mar 12, 2020 at 8:26
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    @Jan: Yeah, we definitely have all sorts of leads on where improvement could be found. Though even once some of those leads, e.g. in bridging macroscopic and microscopic descriptions, are successfully followed, the result almost certainly won't be a complete, correct solution, but rather an improvement that, itself, will have more leads to follow. The "each answer just raises more questions"-sorta thing. (Though I'd note that this is a popular-friendly description -- in truth, we're aware of far more problems than could be listed; the popularly discussed ones are just low-hanging fruit.)
    – Nat
    Feb 5, 2021 at 12:27
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    @Nat why is that? What is the alleged purpose for outing trans people every time they go through passport control?
    – pjc50
    Feb 5, 2021 at 13:24

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