The context of this post is an ongoing discussion concerning the identity of the human person. Previously, I’ve made a distinction between the substance of a thing and the accidental properties which accrue to that thing. This “thing,” in this case, is the human person, which I’ve described as the imago Dei in terms of substance, the accidents being those things which do not determine essential or substantive identity yet change from time to time, i.e. black hair turns to grey, skin becomes tan, etc.
If we consider human nature, in general, in terms of the individual man, the above seems somewhat easy to put together. A man can be the same man substantially even though some of his accidents may change. Easy enough, right? But, this simplicity dissolves whenever we consider gender, or the distinction between male and female. As Christians, we would obviously deny that a person would be the same person if they were able to switch from male to female. Gender, after all, is not only accidental, but seems substantially determinative of a person’s identity, more so than eye color, hair color, skin color, life circumstance, etc.
I believe Aquinas can help sort out this difficulty by making the proper distinctions. In ST, 93.4, Thomas “steel mans” (represents to the best of his ability) the following objection—
It would seem that the image of God is not found in every man. For the Apostle says that man is the image of God, but woman is the image (Vulg., glory) of man (1 Cor. xi. 7). Therefore, as woman is an individual of the human species, it is clear that every individual is not an image of God.
The image of God, in its principal signification, namely the intellectual nature, is found both in man and in woman. Hence after the words, To the image of God He created him, it is added, Male and female He created them (Gen. i. 27). Moreover it is said them in the plural, as Augustine (Gen. ad lit. iii. 22) remarks, lest it should be thought that both sexes were united in one individual. But in a secondary sense the image of God is found in man, and not in woman: for man is the beginning and end of woman: as God is the beginning and end of every creature. So when the Apostle had said that man is the image and glory of God, but woman is the glory of man, he adds his reason for saying this: For man is not of woman, but woman of man; and man was not created for woman, but woman for man.
Therefore, we should consider both man and woman under human nature, while at the same time understanding that, individually, man and woman have more specific, individual natures, i.e. male and female. Man is substantially distinct from woman in that sense, and this is predominantly seen in the distinction between the final causes of either. Man’s end, in terms of the male nature, is God; woman’s end, in terms of female nature, is man (1 Cor. 11:9). But when both male and female are considered under, more generally, human nature, their combined end is God (cf. WSC, Q.1).
So, gender introduces more into the equation. Generally, there is one human nature. More specifically, however, human nature might be considered under male and/or female natures, each of which have distinct ends (purposes, roles, etc.). The same cannot be said with respect to skin color, height, etc. Man’s formal and final causes remain the same regardless of height, skin color, eye color, or any other accidental properties. This is not the case with gender.