Appendix 4.(fn. 222).
The word `nature, taken as the opposite of `reason', has a long history, and bears much the same meaning as that given by its etymology. In Latin, natura [nature] has the same root as nascor [I come to birth], while fusiV springs quite obviously from the verb fuo, `I plant, produce, generate' and so on. Reason, however, is not something that comes to birth or decays. Hence the famous distinction of Plato: all things are divided into those which generate and decay (gigomena), and those which, neither generating nor decaying, are eternal. Such a way of considering what is inherent to the use of words in very ancient languages shows how familiar to the human mind are the truths I have proclaimed about the nature of being. It shows that the system of philosophy which I have proposed has per se the consent of the human race; languages, our oldest and most trustworth y monuments, mirror this consent. I have shown that reason possesses an eternal element which is not the human being, although it is manifested in the human being; it is in no way subjective, although it is intimately united with the subject; finally, it is not a created, finite nature (quod nascitur [that which comes to birth]), but something superior to nature. The opposition between nature and reason, which is found in very ancient languages, is therefore the same opposition that I have endeavoured to establish between subject and object, that is, between created human beings and that ideal being which enlightens them, both without confusing itself with them, or coming to birth or perishing with them. It is the same opposition as that which we find between the intelligent soul and the light that renders the soul intelligent, and in the conjunction between the finite and the infinite, the human and the divine.
But we should also consider the other meanings of the word `nature''. Here I shall quote from Aquinas, whose wonderful gifts included that of ascertaining the meaning of words with great acuteness and precision, a necessary condition for all good logic.
He shows how other meanings of `nature' derive from the most ancient use of the word. According to him, the following are the four meanings which the word `nature' successively acquired: `First, it was employed to signify the generation of living things, that is, their birth. Then it came to mean the intrinsic principle of all movement, metaphorically speaking generation, as we know, springs from an intrinsic principle. It was then extended to mean both the form and the matter of things because the intrinsic principle is the cause of both. Then it was applied to the essence of things because essence receives its completion from form' (S.T., I, q. 29, art. 1). Now, when the Stoics said, `It is the nature of the human being to be rational' and deduced a natural Right according to reason, and when Cicero, following their footsteps, wrote: `Taking what is another's, and augmenting one's own well-being at another's expense, is more against NATURE than death, poverty, sorrow or anything else that can happen to the body or to external things' (De Off., 3, 5), they used the word `nature' in place of `essence', that is, the essence of human beings. Cicero propounded his beautiful opinion - which contains the true principle of the Right of nature - because being rational, and consequently moral, is essential for human beings. And it is entirely in keeping with this essence that one should not harm others, even to help oneself.