Lesson 2: The Philosophy of Nature

For Aquinas, the study of the soul is the primary avenue into the study of human nature. It is the crucial, pivotal inquiry of philosophy, providing us with self-knowledge and urging us to realize and perfect our nature in pursuit of the goods of knowledge and virtue. Aquinas subscribes to Aristotle's teaching on the appropriate order of philosophical pedagogy. The student is to begin with the propaedeutic disciplines of logic and mathematics and then move through natural philosophy to ethics and politics and on, finally, to metaphysics. Where does the study of human nature occur? It is the culminating inquiry of the philosophy of nature, which investigates substances composed of matter and form. Since soul is to body as form is to matter and form is defined in relation to its proper matter, soul must be understood in relationship to body. The study of the soul pertains to natural philosophy from its mode of defining (Commentary on the De Anima, Bk. I, lectio 1). In living things, soul is the animating, organizing, and directing principle of a body. Aristotle's approach is sometimes called "hylomorphism," from the Greek terms for form and matter. This approach differs markedly from the mind-body problem of modern and contemporary philosophy. The latter begins from the supposition that mind and body are separate substances and then proceeds to account for their interaction or from the thesis that mental events are just bodily events, that thinking can be reduced to physiological processes.

In an essay that deftly deploys Aquinas's commentary on Aristotle's De Anima to explicate Aristotle, Martha Nussbaum and Hilary Putnam write,

The mind-body problem...starts from a focus on the special nature of mental activity--therefore from just one part of the activity of some among living beings... Aristotelian hylomorphism, by contrast, starts from a general interest in characterizing the relationship, in things of many kinds, between their organization or structure and their material composition. It deals with the beings and doings of all substances... It asks two questions in particular... How do and should we explain or describe the changes we see taking place in the world?... What is it about individuals that makes them the very things that they are?4

For Aquinas as for Aristotle, the study of the soul embraces all living things and investigates their natures by attending to their habitual modes of operation. Far from setting human beings in opposition to nature, it depicts them as part of nature and proceeds to underscore what is peculiar to the human species.

The study of human nature, then, presupposes some knowledge of nature in general, of its principles and causes. In the second book of his Physics, Aristotle investigates the principles or causes of nature. Most of his predecessors identify nature as the "first constituent or underlying matter," out of which natural things come to be. A common project among the earliest philosophers was to identify an element, say, water or fire, out of which all things emerge. As crude as these accounts may seem, they have the advantage of beginning with the most obvious fact about natural substances: their materiality. But how then do we distinguish different kinds of material substance from one another, say, a "cow" from a "man"? Aristotle suggests that the distinction between the two involves something more than a difference in constituent material parts. Aristotle calls that something more "shape or form." While he holds that natural substances are composites of matter and form and hence that the physicist must include both under the purview of his inquiry, he argues for the priority of form over matter. In the composite, matter is more receptive than active, whereas form is determining and actualizing. To take an example from art, a lump of clay is potentially a bust of Lincoln. It becomes an actual bust only after the sculptor has imposed a shape on it, that is, when the lump receives a determinate form. Indeed, we distinguish, identify, and name things from their forms; that is, not from the mere presence of matter, but from the specific way the matter is configured and organized. Even the lump of clay, which is potentially the bust of Lincoln, is more than mere matter; it has a certain composition, texture, color and so forth which enable us to distinguish it from bronze. Matter may indeed be that out of which things come to be, but the form supplies the reason why the material constituents develop in the way they do. The formal cause is thus intimately related to the final cause, the goal, end, or telos of the process of growth. We implicitly acknowledge the authoritative standards of these causes when we refer to a given instance of a species as immature or defective. Just as the bust of Lincoln without a nose is either incomplete or defective, so too is an apple tree that bears no fruit.

The formal cause is evident, then, both during the development of an organism, and when it is fully formed. Mature instances of species exhibit themselves as organic wholes not as heaps of unrelated parts. The parts themselves are understood in relationship to one another, that is, in the complementarity of their functions and in the way they serve the survival and flourishing of the whole. There is, moreover, a directedness to living things, which is increasingly palpable as we approach the level of the human.

To these two causes, Aristotle adds the initiating or efficient cause and the final cause. His description of the four runs thus:

In one sense a "cause" means (1) that from which, as a constituent, something is generated; for example the bronze is a cause of the statue, and the silver, of the cup... In another, it means (2) the form or the pattern, this being the formula of the essence...; for example, in the case of the octave, the ratio 2:1.... In another, it means (3) that from which change or coming to rest first begins; for example, the adviser is a cause, and the father is the cause of the baby, and, in general that which acts is a cause of that which is acted upon, and that which brings about a change is a cause of that which is being changed. Finally, it means (4) the end, and this is the final cause [that for the sake of which]; for example, walking is for the sake of health. Why does he walk? We answer, "In order to be healthy"; and having spoken thus, we think that we have given the cause. (Physics, II, 1: 1194b25-35)

Now, certain objections (most of which can be traced to early modern philosophers like Descartes, Hobbes, and Bacon, who sought to supplant Aristotle's physics) are commonly raised against the appeal to formal and final causes. We will consider three. The first objection focuses on final causality and alleges that the application of these causes to sub-human beings involves personifying nature, an unwarranted projection of properly human traits onto sub-human beings. Only human beings deliberate about ends and consciously seek to realize goals. To say that plants or snails act for the sake of ends is to ascribe conscious intention to them. The second objection starts with the assumption that all that exists is material things in motion, interacting and producing certain results. On this view, formal and final causes play no verifiable role in experience. The appeal to formal and final causes postulates the existence of "occult qualities," hidden causes that could never be verified by empirical, scientific inquiry. The third worry, which may well be implicit in the first two, is that the search for these causes is naive, superfluous, and unscientific. To focus on formal and final causes is to remain at the level of crude, unreflective common sense and to distract us from serious scientific analysis and experimentation. Besides, even if there are such causes, knowledge of them seems to add nothing substantive to what we derive from the exclusively quantitative accounts provided by the modern sciences.

By way of response, we should note first that nothing in Aristotle's description of formal and final causes eliminates the possibility of seeking explanations in terms of material causes. Indeed, his view is that a form cannot be understood apart from its material subject. Aristotle doesn't want to replace naturalistic explanations but to enlarge our sense of what it means to give such an explanation. In this sense, the second objection, the occult quality objection, is wide of the mark. The form is precisely the organization of the matter. This does not mean that the essences of material substances are transparent to human intelligence. Getting at the essence is difficult, but there is no gulf between the matter of a substance and its form. As we have already noted, the form is not some separate substance, unrelated to matter, but rather the very configuration and organization of the matter, exhibited in the process of growth and in the habitual activities of species. We come to know the essence by attending ever more carefully to the organization and activities of the substance in question. The first objection, concerning an anthropomorphic projection onto nature, also contains a kernel of truth. Final causality, for example, is most evident to us in our own consciously directed operations; indeed, the composition of form and matter is most evident to us in examples from art, where the distinction between the two causes is palpable precisely because the artist introduces from the outside a form into the matter. Thus, in the second book of the Physics, when he introduces the four causes, Aristotle begins with examples drawn from art. This is in keeping with the pedagogical principle stated in the opening of the work that we must begin with what is most evident to us and work toward what is most evident in nature (Physics, I, 1). But the fact that acting for an end is most obvious in conscious, human activity in no way diminishes the presence of final causality in dogs or apple trees. They, too, exhibit a process of development toward an end, although they are unaware of it. Not even in human development, which is directed to an end, is there an imputation of conscious choice or intention. It's not as if a 13 year old chooses to grow 3 inches over the summer.

If, finally, this view is naive, then there may well be some virtue in naiveté. Philosophy should never rest with the obvious, but it ought not to discount it either. Aristotle's approach has the advantage of fostering some level of continuity between our pre-scientific, common-sense experience of nature and our scientific inquiry into the principles and causes of nature. This pre-scientific experience is an ineliminable background for every inquiry and experiment. Can a doctor perform major surgery on a patient without an implicit acknowledgment of the proper functioning of organs like the heart and the lungs? It is a minor point, perhaps, but nonetheless true. On a larger scale, if science is to give an account of itself, of its origin and purpose, it will have to recur to the pre-scientific familiarity with nature, or else its explanation will be merely an unreflective and dogmatic description of what it does and produces, not an account of how we might come to understand and value its inquiry in the first place.

Of course, one of the primary modern motives for rejecting formal and final causes is Darwin's theory of evolution. Although he finally banished these causes, Darwin himself was deeply ambivalent about whether his theory of evolution could do without them. In their absence, it is difficult to use terms like "development" or "higher" and "lower, " terms which imply progress in the direction of what's better and higher and hence seem to involve the notion of a telos or final cause. Classical evolutionary theory wants to concentrate exclusively on antecedent material and efficient causes, whose interaction is the explanatory nexus for change within and between species. But this gives us no ground for saying that one species is higher than another, only that one species is more fit for this or that environment. For Aristotle, we may speak of one species being higher than another in terms of levels of soul; higher souls contain the powers and capacities of lower order souls and integrate them in service of whatever the highest power of the species may be. So animals have both the vegetative powers of plants and the sensitive powers proper to them, while human beings have both of these and rational powers as well. As we ascend the grades of soul, we encounter increased openness to the external world, a greater ability to interact with the world, and enhanced inwardness, a depth of activity and awareness.

Reading Assignment

Aristotle, Physics, II.

Writing Assignment

1. Reflect on Aristotle's four causes by examining examples from art and nature.

2. What is Aristotle's argument (in Physics, II, chapters 8-9) that parts of natural substances develop for the sake of an end, not merely by chance or necessity?

Suggested Reading

Leon Kass, Toward a More Natural Science. (New York: The Free Press, 1985). See especially the chapter on Darwin.


4. "Changing Aristotle's Mind," in Essays on Aristotle's De Anima, ed. A. Rorty and M. Nussbaum (Oxford: Clarendon Press, 1992), pp. 28-9.


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