The best biology, psychology, and philosophy all support an understanding that sex is a bodily reality and that gender is a social manifestation of bodily sex.1 By contrast, “gender identity” is an internal sense of gender.
Sex is a biological reality, referring to an organism’s overall organization towards sexual reproduction. In human beings, just like every other species that sexually reproduces, this organization includes the chromosomes we inherit from our parents and the reproductive organs, systems, genitalia, and hormones that develop as a consequence. As there are two reproductive systems, there are two sexes. This organization isn’t just the best way to figure out which sex you are. It’s the only way to make sense of the concepts of male and female.
Gender, by contrast, is the way one expresses their biological sex. We shouldn’t pretend that there are no differences between male and female, because the biological reality is that there are—we also shouldn’t get trapped in rigid gender stereotypes.
Transgender activists deny that sex is a bodily reality. They argue that one’s perceived gender identity represents who a person really is even if it goes against their biological sex. They deny biological reality by suggesting that biological sex was merely “assigned at birth.”
According to the American Psychological Association, “Gender identity refers to a person’s internal sense of being male, female or something else.”2 It is distinct from either sex or gender. Activists claim it is a person’s “internal sense of gender.” They also assert that it’s more than just male or female; it’s fluid and there is a spectrum of various options beyond man and woman, like “gender fluid,” “intergender,” or “non-binary.”
1. See Ryan T. Anderson, When Harry Became Sally: Responding to the Transgender Moment (2018), chapters 4 and 7.
2. American Psychological Association, “Transgender People, Gender Identity, and Gender Expression,” https://www.apa.org/topics/lgbt/transgender (accessed September 16, 2019), and “Report of the Task Force on Gender Identity and Gender Variance” (2009), https://www.apa.org/pubs/info/reports/genderidentity (accessed September 16, 2019).