Hylomorphism is an account of the natural world according to which corporeal beings are composed of matter and form. The view was first advocated by Aristotle, most prominently in his Physics and Metaphysics. Today, it has been revived by a number of philosophers, notable among them Kathrin Koslicki, Kit Fine, and Mark Johnston.
Today, the view is motivated as a reaction to: physicalism, according to which all there is to reality is the physical; materialism, on which everything is material; and naturalism, which comes in two main forms. Metaphysical naturalism denies the existence of anything above or outside of nature; methodological naturalism assumes metaphysical naturalism as a working hypothesis for philosophical and scientific work, but leaves aside the question of whether it is true. These were the dominant attitudes of philosophers in the English-speaking world for much of the twentieth century; and because of their widespread popularity, both the exact content of and relation between these views has often been opaque.
The positions described in the previous paragraph were most often motivated both i) by the success of the physical sciences; and ii) a desire to have reality be basically comprehensible. Natural science in general and physics in particular, the physicalist thinks, have done a remarkable job explicating the structure of reality in terms of a limited number of basic elements; and since the sciences have gotten along so well without God, souls and other mysterious beings, it’s inductively likely we can ultimately arrive at a complete picture of the world without such beings.
There have always been things the naturalist worldview has struggled to explain: science has little to say about ethics and values, for instance, and the few insights gleaned from empirical psychology on these matters haven’t exactly been encouraging to robust moral realists. But the most potent challenges to the physicalist viewpoint have been internal to the natural sciences themselves. The scientific concern with the possible, necessary, and impossible may not admit explication in terms of the actual world alone; the sets, classes, and numbers figuring so prominently in mathematical physics do not themselves seem to be physical objects; not just any heap of carbon atoms makes up a living being; and advances in computational theory suggest the mind can do things machines can’t even do in principle.
The revival of hylomorphism has been part of this broader reexamination of the commitments of natural science themselves. According to hylomorphists, a list of elements is not enough to explain a chemical compound, a living thing, or even an artifact: one must also add structure – what the contemporary hylomorphist identifies with form.
As the 14th century Parisian arts master John Buridan put it:
‘A composite […] is one per se and composed or mixed out of many elements, […] such that if it is one per se it needs, besides those elements, some other part, sc. form, on account of whose unity it itself is actually one per se.’
In both contemporary and later medieval accounts like that of Buridan, hylomorphism is prompted by the failure of a more materialistic standpoint to account for everything there is. Thus, forms are posited as additional pieces of the universe’s basic inventory, much in the way other non-naturalist philosophies add possible worlds and objects, numbers and sets, minds, phenomenal qualia, or values.
In this way, though, both contemporary hylomorphism and its later medieval analogue remain what I should call ‘broadly materialist.’ The materialist view is not so much defined by a commitment to the existence of only physical things, but rather by a certain way of understanding the question of what there is. The materialist is fundamentally committed to an understanding of this question as one of what reality is made out of. In accordance with certain widespread metaphors in metaphysics today, the metaphysician is after the basic furniture of the world, its building blocks, an inventory list for the universe. Thus, the person who posits structures, forms, numbers, minds, etc. still remains in the grip of a broadly materialist way of thinking. The ancient Greek materialist Antiphon thought everything was earth, air, fire and water. The contemporary hylomorphist merely regards Antiphon’s base set as insufficient.
When forms are posited in the above-mentioned fashion, an ambiguity arises in the meaning of the term ‘being’ and its synonyms, granting a broader and a restricted sense. On the broader sense, the term is used to refer to everything there is. But in the restricted sense, the term continues to refer to that which is most properly basic, the paradigmatic cases of such ‘building blocks’. Hence, it becomes possible to pair the term with another contrasted with it: ‘being and value’, ‘appearance and reality’, ‘word and object’, ‘mind and nature’, ‘being and structure’. In this way, the more restricted materialist outlook reasserts itself in its fittingness as an answer to the broader materialist’s way of posing the question. In identifying the material with the real in its most proper sense, the new structuralism effectively cedes the materialist outlook Aristotle himself set out to refute.
The primary disagreement between Aristotle and Antiphon is not one about what things are, but one of what being is. As I write this, I sit on a train. Typing on my computer. Next to three other people all playing with their various gadgets. In typing these simple words, I name what is before me, calling it to your attention. I describe what is. I do not say, ‘three structured carbon-things’, but ‘three people’. And in doing so, I name what they are, and describe the shape and currents of my surroundings. When I get home, I will not call my home ‘wood’ or ‘sticks’, but a house. Nor will I call the trees in front of my house ‘wood’ but ‘trees’. In all of these cases, I name the beings around me not by reference to building blocks, but by calling them what they are. And in the simplicity and obviousness of this last point, the materialist outlook is ceded as having nothing to do with what it means to be. Rather, the being of beings is given in the shapes, limits, or forms wherein they present themselves to us: as human, sitting, reading, chewing gum. Even in cases where I wish to highlight precisely the composition of a thing, I do not identify the thing with its elements: the cake is made out of flour, milk, egg, and sugar; and it is the cake that is so made. in calling the cabinet ‘wooden’ rather than ‘wood’, I name its makeup as something that belongs to it, rather as the thing itself; and it is the cabinet that is so composed.
The simplicity of these points goes to show us how much room our understanding of being has to grow.
 ‘Hylomorphism’ comes from the Greek hyle (= matter), and morphe (= form).
 John Buridan, Questions on Aristotle’s Physics, Bk. 1, q. 9, ad 2.