Courageous gender-critical philosophy Alex Byrne asks: What is Gender Identity? He works his way through some intellectually lazy non-definitions, but eventually arrives at the following claims which he calls “the standard picture” of gender identity:

• Everyone has a gender identity, which is usually stable. Non-transgender people have gender
  identities that match their sex.
• Transgender people — in particular, MtF and FtM transsexuals, or transgender/trans women and transgender/trans men — have gender identities that do not match their sex.
• A mismatch between sex and gender identity causes gender dysphoria.

OK, those are the claims gender true believers believe, at least many of them. But are they true? Here’s where it gets interesting. Byrne objects that the second is clearly false.

Do all trans women have female core gender identities? No. It is easy to find trans women who say that they are male (and not female) — or men (and not women). Taking them at their word, they do not have a female core gender identity.

If the second claim is false, then this sort of “gender identity” can’t be the explanation of what makes trans people trans. Why? Because some are trans, and yet don’t have the mismatch described by the second claim above.

That right there is a shocking enough conclusion.

But Byrne knows that there is supposed to be something called “gender identity” which is supposed to explain all trans people. So he keeps searching.

Is there another kind of gender identity that all transgender people have, and which does not match their sex? Specifically, is there a kind of “female gender identity” that is shared by trans women? Here are some candidates: a sense of kinship with females as a group, a female-typical psychology, satisfaction at being socially treated as a female, a tendency to conform to the norms of female behavior, and a tendency to emulate female stereotypes.

You’ll have to read the rest of his post to see what he concludes about these.