ABSTRACTRecently an acrimonious debate has emerged about transgenderism. Trans-activists defending the full spectrum of the latter have advocated a form of identity politics based upon individual self-definition. However, gender-critical feminists have disputed the legitimacy of these bids for self-determination, especially when considering men who are claiming to be women. These contrasting positions are examined and their political implications explored. The focus of the paper is on the intransitive aspects of sex and the transitive aspects of gender. The former, with rare (...) exceptions, is a binary whereas the latter is open to social negotiation and variation. The article argues that the gender-critical position is broadly aligned with critical realist philosophy, though the counter view is represented in order to clarify this point of reflection. It ends with a discussion of the ‘trans debate’ and the public policy development emerging in its wake. (shrink)