Nature is a word of varying meanings, which can best be understood if we consider its various opposites. The Natural is the opposite of the Artificial, the Civil, the Human, the Spiritual, and the Supernatural. (C.S. Lewis, The Abolition of Man, ch 3)How can we distinguish these varying meanings?
We'll start with David L. Schindler's historical-etymological exposition in "The Problem of Mechanism."
The term physics, comes from the Greek physis and thus in turn from the verb phyo, which means "to bring forth, produce, put forth; to beget, engender, generate" and so on (Lidell and Scott Lexicon). And physis is rendered into English as "nature," which comes from the Latin "natura," and thus in turn from the verb "nascor" which, like "phyo," is also associated with giving birth. We can see developed in Aristotle the full meaning of these initial etymological considerations.Dr. Schindler distinguishes
...two fundamentally different ways in which the terms physis (nature) and physics have been understood in the history of Western thought. The first of these is represented in Aristotle, in what may be called the classical Greek view. The second is represented in Descartes, in what may be called the classical modern view....Since the modern view is more familiar to us, we will explore these in reverse chronological order. The modern (or Cartesian) understanding is "nature as matter," as William A. Wallace calls it his The Modeling of Nature. Lewis speaks of nature in this way in chapter 2 of The Four Loves and in all but the end of The Abolition of Man. Nature as matter, Schindler writes, is devoid of any internal activity and
essentially inert (or as Descartes says, in repose). To put another way, any activity to be ascribed to nature (matter) must now be of an external sort.As Lewis puts it,
Nature seems to be the spatial and temporal, as distinct from what is less fully so or not so at all. She seems to be the world of quantity, as against the world of quality; of objects as against consciousness; of the bound, as against the wholly or partially autonomous; of that which knows no values as against that which both has and perceives value; of efficient causes (or, in some modern systems, of no causality at all) as against final causes. Now I take it that when we understand a thing analytically and then dominate and use it for our own convenience, we reduce it to the level of 'Nature' in the sense that we suspend our judgements of value about it, ignore its final cause (if any), and treat it in terms of quantity.Schindler writes that, in contrast,
...nature for Aristotle is not matter: for nature in the full and proper sense for Aristotle is something actual and matter in its basic meaning is not actual—it is what has the capacity for becoming actual. It follows that nature in its full and proper sense must be—not matter—but that—the act or activity—in virtue of which nature, and hence matter, are said to be actual.
Wallace distinguishes Descartes's passive "nature as matter" from Aristotle's active "nature as form":
Unifying form, no less than the underlying matter, is the internal source from which all such activities ultimately spring. Behaviors, actions, and reactions are natural for a substance precisely to the extent that they proceed from within it, and thus from its matter and form as its basic intrinsic constituents. (11, 1.3)
Or as Schindler says,
for Aristotle, proper understanding of nature, of matter as an actual part of nature, requires an understanding of what it means to be in the most fundamental sense (ousia), and this in turn is seen to require understanding of such features as immanence (immanent source of the activity in terms of which something is said to be actual, to grow, to change, to move), form (act of forming), end (act of finalizing), actuality or activity, and completeness or wholeness.To summarize, we use the word nature in a range of ways, bounded it seems by the usages of Aristotle and Descartes exemplify. Aristotle saw nature as primarily the inner activity of a thing that perfected it and formed it to its ends, while Descartes saw nature as definitionally passive, relegating activity to unnatural imposition from without.
A further distinction is necessary. Schindler describes how Aristotle's nature-matter needs always to be joined to nature-form:
...(a) that matter is a relative concept; it is something which can properly be understood in its actuality, only and always in relation—to nature in a fuller, proper sense; secondly, (b) nature, that in relation to which matter takes its full meaning, is characterized by act or activity which is immanent, formal, final, unifying, and complete or whole. This understanding of physis has often been called organic or organismic. These terms seem to me apt, since they are commonly taken to; be characteristic of organisms i.e., the immanent activity of form and finality, internality of relation among the distinct "parts" of the organism, and consequently a wholeness of the organism which is distinct from the sum of its "parts."Whereas Descartes's claims are
....(a) that matter is an absolute concept, something apart from, not-relative to, anything "more" like Internal—formal and final—activity; (b) that nature, now absorbed into matter in this way, is whole (in any of its instances) only in the sense of being a collection which is exactly the sum of externally interactive parts.Thus we come to Descartes's description of the human body-soul composite which is commonly caricatured as "A ghost in a machine." The ghost is inside the machine, but not integrally or organically united to it. Regardless of the faithfulness of this summary, the conclusion is grossly mistaken. As Aristotle says, the soul is the form (or nature) of the body. This truth is the reason that a human body without a soul is not a human being, but a corpse.
With the Cartesian understanding, the human intellect can only be unnatural. Man himself is unnatural to the extent that his intellect guides him, and he is natural to the extent that external forces control him. This reasoning explains why moderns see giving in to their desires (no matter how base, no matter into what a sordid state of unhappiness it draws them) is "natural," while exercising self-control to follow the course that reason says will lead to happiness (in the larger, fuller sense) is "unnatural."
As usually confused pop-star Sheryl Crow poignantly sings by some unknown grace:
Benedict Ashley, Theologies of the Body: Humanist and Christian, (Braintree, Mass.: The Pope John Center, 1985).
David L. Schindler, "The Problem of Mechanism," in Beyond Mechanism: the Universe in Recent Physics and Catholic Thought, ed. David L. Schindler (Lanham, MD: University Press of America, 1986).
William A. Wallace, The Modeling of Nature: Philosophy of Science and Philosophy of Nature in Synthesis (Washington, D.C.: Catholic University of America Press, 1996)