Gender reassignment surgery does not change a person's biological sex. It is impossible for Miss Cossey to bear a child. Yet, in all other respects, both psychological and physical, she is a woman and has lived as such for years.
The fact that a transsexual is unable to procreate cannot, however, be decisive. There are many men and women who cannot have children but, in spite of this, they unquestionably have the right to marry. Ability to procreate is not and cannot be a prerequisite for marriage.
The only argument left against allowing Miss Cossey to marry a man is the fact that biologically she is considered not to be a woman. But neither is she a man, after the medical treatment and surgery. She falls somewhere between the sexes. In this situation a choice must be made and the only humane solution is to respect the objective fact that, after the surgical and medical treatment which Miss Cossey has undergone and which was based on her firm conviction that she is a woman, Miss Cossey is psychologically and physically a member of the female sex and socially accepted as such.
It should also be borne in mind that Miss Cossey has no possibility of marrying unless she is allowed to marry a man as she wishes. It would be impossible, both psychologically and physically, for her to marry a woman. There would certainly also be doubts as to the legality of a marriage of this kind.