What Makes a Living Body One Thing?
Aristotle, material organization, and the question of form
A living body contains many different materials. What makes them one living thing?
A list of an animal’s ingredients can be remarkably detailed and still leave that question unanswered. We might identify its tissues, cells, and chemical constituents without explaining how they sustain a single life. The arrangement matters, but so do the activities through which the parts maintain one another and the animal continues to exist.
This problem lies at the center of my article, Organization Without Formal Priority? Mechanistic Materialism in Aristotle’s Metaphysics Z–H. Aristotle gives us a powerful reason to reject the idea that a living thing is simply a collection of ingredients. My question is how far that argument takes us.
What an inventory leaves out
In Book Z, chapter 17, of the Metaphysics, Aristotle considers the difference between a syllable and its letters. Knowing which letters are present does not yet explain their unity as a syllable. Similarly, identifying the materials that make up flesh does not explain why those materials constitute flesh.
Adding another ingredient does not solve the problem. The larger collection would still need an explanation of its unity. Aristotle calls our attention to form: the principle through which the materials constitute a determinate whole. In this discussion, form concerns what a thing is, including its characteristic capacities and organization; it means more than its outward shape.
Book H develops the account through organization, the capacities of appropriate matter, and the relation between potentiality and actuality. Aristotle does not require a further bond to attach matter to form. His account therefore should not be pictured as a mysterious extra object somehow holding the body together.
Can organized matter do the explaining?
The strength of Aristotle’s argument creates a further question. Once we agree that ingredients alone are insufficient, must we also agree that form has explanatory priority over organized material activity?
By “explanatory priority,” I mean that the nature of the whole explains what its parts are and why they have their characteristic powers, while the organized material parts cannot fully explain the whole in return. That is a stronger claim than saying organization matters.
A contemporary mechanistic materialist can accept that organization is indispensable. On this view, a living system’s capacities arise through material components acting together at several levels. Parts may acquire powers through their relations with other parts. Feedback, regulation, development, and repair belong within the explanation.
This is a modern alternative used to test the argument. I am not suggesting that Aristotle anticipated contemporary biology or would have accepted its materialist interpretation.
The heart makes the problem concrete
Consider the heart and circulation. Listing muscle, valves, chambers, blood, and vessels does not explain how circulation occurs. A mechanistic account describes coordinated contractions, electrical signals, pressure differences, and the support supplied by other bodily processes. It also explains how disruption of those relations can impair circulation.
Yet the Aristotelian can press a deeper question: why identify these structures as the relevant parts? A body can be divided into countless spatial regions. A valve counts as an explanatory part because of its role within an organized activity. Have we explained that organization, or relied on an understanding of the whole to select the parts in the first place?
A failing heart sharpens the difficulty. It can remain a heart even when it pumps poorly. Its function cannot simply mean whatever it happens to be doing. We need an account of why pumping is its characteristic work and why some departures from that work count as malfunction.
The materialist can appeal to development, evolutionary history, and the reciprocal processes through which the organism sustains its organs and those organs sustain the organism. The challenge is to show that these relations explain unity and function without quietly assuming the very whole they are meant to explain.
Where the argument remains open
There is an equally important demand on the defender of formal priority. Defining a heart by reference to the living animal does not, by itself, establish that the animal’s form is the ultimate explanation of the material processes involved. How we identify something, what it requires to operate, and what ultimately explains it are connected questions, but they are not interchangeable.
My conclusion is therefore qualified. Aristotle shows why an inventory cannot explain a living whole. A richer material account must still explain why its interacting processes constitute one organism, why its parts have functions, and how the individual persists as its materials change. Its success cannot simply be presumed. Neither can its failure be inferred from the inadequacy of a list of ingredients.
Can organized material activity explain why there is one living thing, or does that activity itself require a prior account of what the whole is?
That is the question I take from Aristotle. It remains demanding because both sides recognize the reality of organization. The disagreement concerns what explains it.
Read the article’s abstract and download the full manuscript →