One important idea we are trying to target with the word “nature” is what is divided from reason, where “reason” means “decided upon” or “chosen”.
I have no desire to critique this sense of nature, only to tease out some problems it creates for our attempts to understand who we are.
1.) So far as things depend on our choice or decision they are seen as being fundamentally conventional as opposed to true. Money, systems of measurement, the words of a given language, whether a man is king, etc. are all seen as being indifferent to being one thing as opposed to another, at least so far as they are dependent on choice. So we have to seek some “truth about ourselves” outside of the rational in the sense of decided upon or chosen.
2.) But then what if we take “rational” as “true” or perhaps “moral”? In this sense we are we need to recognize that what is outside the rational needs to also be rational.
3.) The first answer is that this is no big deal. Words have multiple senses. There is nothing odd in having to describe something as X is one sense and non-X in another, especially with a words that have as many meanings as reason and nature. Sure, but what about the details beyond the pure negation? Why do the ambiguities in our ideas of reason lead us to these contrary significations? A Thomism account is that we are only rational by participation, i.e. it is a condition of our being rational at all that this reason depend for its existence on things that are not rational.
The truth of the Platonic idea, even in its crudest form of separated couches in the heavens, is this: nothing other than God can exist apart from being intrinsically combined with its opposite. The Platonic idea of X is just what X is and nothing more that real X’s need to exist. Taken in this way, there is no contradiction between Plato and Aristotle. Aristotle’s objection that some forms can only be in sensible matter is, in Platonic terms, exactly what is meant by a form existing by participation. Neither P or A think this is the only way a form can exist, however, since both hold it can exist in knowledge.
4.) Persons are rational. But rational is materially “cognizant” or “aware” and formally “self-directed”. But all the elements of personality are things of which we are non-cognizant and which we don’t self-direct. No one self directs his own extraversion, degree of intelligence, openness to experience, pessimism, preference for the personal. etc..
5.) Take our ambivalence about sexuality. We are uncomfortable both with calling it chosen and with calling it natural/ of personality. The chosen is too arbitrary, the natural too inflexible. For my own part, I can’t relate to it as anything but natural/or of personality, and I’m baffled by testimonials that give it more ambivalence (Roger Lancaster claims that not only he, but all his heterosexual friends experience periodic homosexual desires, though I can no more understand this than what it is like to be a bat.)