Debbie Hayton is a physics teacher at a school in the West Midlands, in Britain. She is a vocal campaigner for trans rights, but she argues that self-identification is an unwise step to take because it risks the credibility of the gender-recognition process. Trans people need more than feelings to protect them from an uncertain future. Follow her on Twitter @DebbieHayton.

When Tara Wolf assaulted Maria MacLachlan at Speakers’ Corner on September 13th 2017, a social-media dispute between transgender activists and radical feminists burst out onto the streets of London. Ms MacLachlan, a 60-year-old woman, was going to a feminist meeting that had been forced to move to a secret venue after protests by a group of transgender activists that included Ms Wolf, a 26-year-old trans woman.

Tensions had been raised three months earlier, when Britain’s government announced that it would consult the public on changes to the Gender Recognition Act of 2004, which sets out the steps transgender people must take to get their new gender identity recognised in law. The proposals included gender self-identification, effectively allowing applicants to change their legal sex by simply declaring their intention “to live in their preferred gender” for the rest of their life. They would no longer have to provide medical reports attesting to gender dysphoria, or evidence that they had lived in the target gender. The proposals proved more controversial than the government had perhaps expected. Nine months on, the dispute shows no signs of resolution. The consultation was delayed repeatedly, raising the temperature in an already heated environment.

I am a teacher and I encourage my pupils to think critically and judge arguments by the supporting evidence. Sadly in this debate, emotion has eclipsed reason and seemingly contradictory assertions, namely “woman means adult human female” and “trans women are women” are hurled back and forth without any progress towards a shared position. Future historians may see this as a clash between postmodernism and facts: the facts of life, namely sex and reproduction, on the one hand, and the idea that sex, or at least gender, is defined by thoughts and feelings rather than bodies. In the meantime, however, for trans people like me the debate is personal and the stakes are enormous. I transitioned six years ago to be freed of the chronic and debilitating effects of gender dysphoria. My goal was to carry on teaching and stay out of the press. That strategy was partly successful: I still work in the same school, and Sir became Miss. But I set aside my desire for privacy to speak out at this crucial time. The rights, protections and identities of trans people are being gambled, not in a court of law but in the court of public opinion. From a trans perspective, it is superficially attractive to base arguments on the concept of an innate gender identity that drives our character and personality. If we have a female gender identity then we are female, while people with a male gender identity are male. It’s simple and it’s empowering. Should our bodies not match our gender identity, then our thoughts and feelings trump our chromosomes and genitals. Arguably, this line of thinking leads to the conclusion that trans women like me are not only women but also female, and have always been female. If that is so, the privileges and protections that society has granted to women—for example, separate sporting events, literary competitions, scholarships, and selection processes such as all-women shortlists—would be ours by right. But gender identity is not easy to define, let alone prove. Even legislators have been forced into circular reasoning. For example, the state of Massachusetts defines it as “a person’s gender-related identity, appearance or behaviour, whether or not that gender-related identity or behaviour is different from that traditionally associated with the person’s physiology or assigned sex at birth”. This, to me, is not only circular but sexist, as it assesses behaviour against stereotypes.

Legislation recently adopted in Scotland adopts a different philosophy. Rather than declare that trans women had always been female, the Gender Representation on Public Boards Act 2018 redefines the word “woman” to include a person who “is proposing to undergo, is undergoing or has undergone a process for the purpose of becoming female”. Perhaps understandably it does not explain how it is possible for someone to change sex. Nor does it specify the nature of the process.

So can a person born with a male reproductive system become female, or claim to have always been female? And can they support those claims with an argument? If state legislatures cannot define gender identity objectively, there seems little hope for individuals. It is not surprising, then, that trans people react defensively when those claims are challenged. Thankfully, most are more restrained than Ms Wolf, but those seeking to base their rights and protections on their own feelings of self are going to feel that their identities are under threat.

Trans people need better than this. Many feel under siege even where society is liberal and accepting. Feminists can be robust in their approach, but they do have reasonable concerns: women would certainly be affected by a changed legal definition of what it means to be a woman. If future society becomes more conservative and dismissive, the outlook for trans people could become grim. Even if rights and protections are enshrined in law, they have little value if people do not respect them. The requirement to produce objective evidence might be seen by some as an affront to our dignity, but it justifies our claims without relying on our feelings or self-declared identities.

If gender identity is unprovable and adherence to sexist stereotypes is unacceptable, then on what can we base our claims? Unless we deny any commonality between human beings and every other species of mammal, people of the sex class that produce ova are female and those whose sex produces sperm are male, and we need one of each to propagate our species. It might be possible to argue that someone could become female if they change their hormone regime and undergo gender-reassignment surgery: our legal sex is certainly determined initially by a cursory glance at our genitals straight after birth. However, unless we accept that a male person whose hormone levels and sex characteristics are changed against his will also becomes a female person, the argument still rests on feelings.

The only objective measure that remains for dividing humanity in two is biological sex—that is, our role or potential role in the reproduction of our species. But this leaves trans people in a very vulnerable position, and not on the side of the line that they would prefer. Although we can’t change our biological sex, trans people have been living happily in a manner analogous to the opposite sex for many years. In Britain, since the Gender Recognition Act was enacted they have also been able to change their legal sex to protect their privacy and allow them to acquire many of the rights and protections granted to the opposite sex, most notably the right to marry as a member of that sex. They have benefitted and society has benefitted. People more comfortable with themselves are likely to contribute more to society.

The system works because it is based on objective evidence, crucially a clinical diagnosis of gender dysphoria and those medical reports. A medical practitioner testifies that changing legal sex is necessary to promote mental wellbeing. That is priceless in a world where truth is increasingly held to be relative and different people hold different truths. In the trans debate those truths are both contradictory and contentious. If people with male reproductive systems can declare themselves to be trans women, and trans women are women, then female reproductive systems no longer define the class of people known as women. This is tortuous language but necessary at a time when basic definitions are challenged in social media bubbles.

Trans people have to live in the real world, where people do not need tortuous language to distinguish between men and women, and the key evidence is not what's in our heads but what's between our legs. We need more than feelings to counter that. If we abandon the testimony of experts, we may find ourselves at the mercy of whoever shouts loudest.

That is no way to live. It would be better to abandon the push to self-identify legal sex and look for progressive changes that make the process of gender reassignment simpler without damaging its credibility. More generally, we need to be intellectually honest. I am not female and I know that I cannot become female, but I can and do live in a way analogous to the way that women live. I make no claims I cannot justify and my life is better for it.

This is part of a two-week discussion on transgender issues, with ten contributors. The other contributions are available here.