Historically it is an interesting question. It harks back to the enlightenment, when Descartes asked “but how do we really know?” And when no one gave him a swift kick in the balls and asked “do you know if that hurts?” The problem began.
What came out of Descartes was a shift in philosophy, where the main subject was no longer how is it than things can be, to how do we really know? This leads to (broadly) two schools of thought: rationalism and empiricism.
Then a very very clever fellow called Immanuel Kant (pronounced with ‘u’ not ‘a’ for all those undergrads who have to battle through the critique of pure reason) came up with a shocking conclusion. Thinking that both rationalism and empiricism were wrong, that they should not be at odds with each other (but really was a rationalist) he came up with what is referred to as the “Copernican Revolution” in philosophy.
his revolution was this: always before we have assumed that reality was there, and we have access to it. Instead, what if we don’t? We have instead a manifold of rational faculties that impose categories and criteria on reality that make it intelligible? Space and time are not out there, they’re in your mind man!
So Kant was attempting to come
up with a unified theory of being- that solved the Cartesian problem of knowledge by answering: we know through the structures of rationality (more or less, it’s more complicated than that but w/e).
the problem with this is he had overcome the rationalist/empiricist divide but created another analogous divide: the subject/object.
we are all “noumenal” objects (objects in reality as we are) but can only know other objects through the phenomena (things as they appear). But the interior reality of what things are, their essence, is closed to us. Phenomenology attempts to overcome this by treating the subject as an object we can know noumenally but it has issues.
On the basis of this, you have post Kantian philosophers who argue that reality is constituted in all sorts of ways. Foucault argues that it is in power structures. Derrida in the subjectivity of the person, etc etc.
all of this though comes down to: reality, certainly the reality of others and probably the reality of ourselves is not known, and worse, cannot be known. Therefore the subject cannot be categorised. The subject is constituted in themself. Their authentic self is realised only by the (journey, drugs, w/e bs you like). Which means things like “sex” are arbitrary categories imposed. Worse, as Foucault suggested, (this is called post structuralism) structures of the elite are maintained by control over language. Therefore language is power. It gets weird. The TRA claim that calling a trans woman a man is LITERAL violence suggests to me that at least one of them was a student of post modern philosophy.
this is basically it: by insisting on your own use of language, or insisting that you have access to the reality of that person, you are inflicting upon them your own subjectivity, which is after all no more valid than theirs. Because we can’t know reality. So identity politics is simply the latest incarnation of the same thing.
Someone really needed to kick Descartes in the nuts.