I will use Robert Eads in order to demonstrate a number of complications which arise from a dogmatic male/female binary and the other possibilities which such a binary excludes:
1) If a man must possess the body of a man, then Eads became a man the moment doctors constructed a penis for him.
If this is the case, then what might his gender have been considered to be between surgeries? If men are subject to this definition of gender then certainly a woman might be too. What is the gender of a human lacking the breasts of a woman but also the genitals of a man, as might a transgendered woman who did not perform the second surgery required for a sex change. Gender, in this case, is dictated entirely by biology, viz. the physical appearance of one's body.
2) If a man must possess the body of a man at birth, then Eads is not a man and it is not possible for him to ever become one.
This belief would appear to imply that those who are born with the biological characteristics of one gender are irrevocably endowed with the thing that is that gender; hence one is essentially a man if and only if one is born a man, for only in this way would one satisfy the condition of essence of required for the being of one gender as opposed to any other. This distinction is more metaphysical (or perhaps spiritual) than physical. As arbitrary and unforgiving as it may sound, the idea of an essential gender predetermined at birth appears to be a common belief among critics of transgendered individuals.
3) If a man must simply know or believe that he is a man, then Eads became a man the moment he thought himself to be a man.
This possibility makes secondary any references to biological characteristics and also hearkens back to medieval perceptions of homosexuality in Europe, which judged that homosexuals were those individuals whose minds were of a different gender than their bodies. Accordingly, this belief system attaches gender to one's mind or beliefs of the body, and all that is required is for one to believe and maintain the belief that one is a specific gender as opposed to any other gender in order to make the distinctions relevant. This belief is problematic, for what would happen if a person were convinced that they were neither male nor female? Or perhaps a person who only temporarily entertained the idea of being transgendered? If I believe I am a man one day, but then later realize that I am in fact female later in life, did I at all change my gender? Can gender really be so subject to whim?
4) If all that is required to be a man is to simply to act as society believes a man should, then Eads became a man the moment he started to behave as one.
This distinction differs from the previous, for instead of the self dictating its own gender, the judgment is instead made by The Other and society. With this distinction, it becomes possible for me to believe that I am one gender and everyone else that I am an entirely different gender; the difference being that the gender I believe myself to be is irrelevant and instead the gender that everyone else believes me to be is relevant. This binary is also problematic, for if society determines such distinctions based upon the images, stereotypes, and myths which dictate its beliefs. It might therefore be possible for me to be judged a woman in one culture, a man in another, and perhaps something else entirely in a third context. The changing definitions of gender are also another factor, for what was once thought masculine in one time might not necessarily be considered masculine in another time.
Perhaps my analysis excludes several other possibilities which were never mentioned, but I only attempt this exercise to demonstrate my point. None of the aforementioned distinctions appear to be satisfactory to the case of Robert Eads but perhaps these points betray an ambiguity in the methods which we use to distinguish one gender from any other, or the entire idea of gender as whole.