The Role of Material and Formal Causes in Metaphysical Being

In metaphysical philosophy, understanding what makes a thing what it is requires more than pointing to what brought it into existence or what purpose it serves. It demands looking inside the thing itself – at its internal composition. This is where material cause and formal cause come in. These two intrinsic causes, first systematically articulated by Aristotle, explain how beings are constituted from within. The material cause deals with what something is made of, while the formal cause deals with what makes it the kind of thing it is. Together, they form the backbone of a metaphysical framework that has shaped Western philosophy for over two millennia.

What are intrinsic causes? 🔗

Before exploring material and formal causes individually, it helps to understand why they are called intrinsic causes. Aristotle identified four types of causes – material, formal, efficient, and final – each answering a different “why” question about a thing’s existence. Among these, material and formal causes are classified as intrinsic because they are internal to the thing itself. They are the constituent principles that make up a being from within.

The efficient cause (the agent that brings something into being) and the final cause (the purpose or goal of a thing) are extrinsic causes – they operate from outside. As Thomas Aquinas explains in his On the Principles of Nature, matter and form are intrinsic because they are parts that constitute the thing, while efficient and final causes are extrinsic because they lie outside the thing. This distinction is fundamental: to understand what a being is, we must first understand its intrinsic composition.

Material cause: the substratum of potentiality 🔗

The material cause answers the question: “What is this thing made of?” At its simplest, the material cause of a statue is the bronze or marble from which it is carved. The material cause of a table is the wood from which it is built. But material cause, in its metaphysical sense, goes far deeper than identifying raw ingredients.

Matter as potentiality 🔗

For Aristotle, matter is not just physical stuff – it is the principle of potentiality. Matter represents what a thing can become. A lump of clay, for example, has the potential to become a vase, a bowl, or a figurine. The clay does not determine which of these it will become; it simply holds the capacity for multiple outcomes. This is what Aristotle means when he describes matter as something indeterminate but determinable.

According to the Stanford Encyclopedia of Philosophy, Aristotle introduces matter in the Physics to account for changes in the natural world, particularly to explain how substances come into existence even though nothing comes from nothing. Matter serves as the underlying substrate that persists through change. When a block of marble becomes a statue, the marble endures – but it takes on a new determination.

Prime matter and the deepest level of potentiality 🔗

Aristotle takes this concept even further with the notion of prime matter (prōtē hulē). If we keep asking “What is this made of?” – breaking wood into fibres, fibres into chemical compounds, compounds into elements – we eventually reach a level of pure, undifferentiated potentiality. Prime matter has no qualities of its own. It is not any particular thing; it is the pure capacity to become something.

As Britannica notes, prime matter cannot itself be a fully actual being because a being already is and does not need to become. Prime matter is a being “in potency” – passive and indeterminate. It requires an active, determining principle to make it into something definite. That determining principle is the formal cause.

Material cause and change 🔗

The material cause also plays a critical role in explaining change. In Aristotle’s framework, change is the transition from potentiality to actuality. The material cause provides the ground for this transition. A seed can grow into a tree because the seed, as matter, carries the potentiality for that transformation. Without the material substratum, there would be nothing to undergo the process of becoming.

This connection between matter and change operates on two levels. At the accidental level, a substance changes its properties while remaining the same kind of thing – a marble block changes shape when sculpted, but it remains marble. At the substantial level, one kind of substance transforms into an entirely different kind – as when food is digested and becomes part of a living organism. In both cases, the material cause accounts for why change is possible, since it is the principle of potentiality present in every physical substance.

Formal cause: the principle of actuality 🔗

If the material cause tells us what something is made of, the formal cause tells us what something is. It answers the question of identity and essence. The formal cause is the structure, pattern, or defining characteristic that makes matter into a specific kind of thing.

Form as essence 🔗

For Aristotle, the formal cause is closely linked to the concept of essence – what it means to be a particular kind of entity. The formal cause of a human being, for instance, is not merely the arrangement of flesh and bones. It is the rational soul, the organising principle that makes a collection of biological materials into a living, thinking person. As the Stanford Encyclopedia of Philosophy explains, the formal cause responds to the question “What is it?” and what is singled out in the answer is the essence of the thing.

This means the formal cause is not simply the external shape of an object. A bowl’s formal cause is not just its round, concave shape – it is the capacity to hold liquids, the functional essence that makes it a bowl regardless of whether it is made of ceramic, metal, or wood. Shape is often an accident; essence runs deeper.

Form as the principle of determination 🔗

Where matter is indeterminate and passive, form is determinate and active. Form is what actualises the potentiality of matter. Without form, matter would remain a shapeless, undefined potentiality – never becoming any specific thing. As the Thomistic Philosophy Page explains, form is the principle of actuality that accounts for each thing being the kind of thing it is, while matter is the principle of potentiality – the capacity to become something other than what it currently is.

Consider bronze. As raw material, bronze has the potential to become a bell, a coin, or a statue. It is the form – the specific design imposed upon it – that determines which of these it actually becomes. The form does not simply decorate the matter; it constitutes the thing’s very identity.

Substantial form vs. accidental form 🔗

An important distinction in this discussion is between substantial form and accidental form. A substantial form is what makes a thing the fundamental kind of entity it is. The substantial form of a dog is what makes it a dog – its animating principle, its canine nature. An accidental form, by contrast, is a non-essential quality: the dog’s colour, size, or the curl of its tail.

Thomas Aquinas developed this distinction extensively. For Aquinas, each material substance has one substantial form that gives it its nature. If that form is lost, the substance is destroyed – it undergoes substantial change. A living tree that dies loses its substantial form (the soul, or life-principle); what remains is no longer truly a tree but a collection of decaying materials. Accidental changes, on the other hand, alter a thing’s properties without destroying its essential nature.

How material and formal causes work together 🔗

The real philosophical power of these two causes emerges when we see how they function in relation to each other. Neither matter nor form exists independently in the physical world. Every concrete entity is a composite – a union of matter and form. This doctrine is known as hylomorphism, from the Greek words hylē (matter) and morphē (form).

The inseparability of matter and form 🔗

Aristotle contends that every physical object is a compound of matter and form. You cannot have matter without some form – even a shapeless lump of clay has the form of “lump.” And you cannot have form without matter (at least in the physical world) – a blueprint without materials produces nothing. The two principles are correlative: matter is that which receives form, and form is that which actualises matter.

This mutual dependence distinguishes Aristotle’s position from Plato’s. Plato held that Forms exist in a separate, transcendent realm, independent of the material world. Aristotle rejected this view. For him, forms are not extrinsic models existing somewhere beyond physical reality – they are intrinsic principles embedded within things themselves. A horse’s form does not float in an ideal world; it is realised in the horse, shaping its matter into a living, functioning animal.

Potentiality and actuality in being 🔗

The interplay between material and formal causes maps directly onto the metaphysical concepts of potentiality and actuality. Matter corresponds to potentiality – the capacity to become. Form corresponds to actuality – the realisation of that capacity. Every existing thing is a blend of these two: it is actual in some respects (determined by its form) and potential in others (grounded in its matter).

This framework explains why things can change without ceasing to exist entirely. When water freezes into ice, the underlying matter persists while the form changes. The water’s matter had the potentiality to take on the form of ice, and through the process of freezing, that potentiality was actualised. The material cause provides continuity through change; the formal cause provides the new determination.

The unity of substance 🔗

One of the deeper questions in hylomorphism is: what makes a composite of matter and form a single unified thing rather than two things stuck together? Aristotle’s answer, as developed by Aquinas, is that matter and form are not two separate beings joined by some external bond. Rather, they are two incomplete principles that together constitute one complete substance. Matter, by itself, is not a “thing” – it is pure potentiality. Form, by itself (in the material world), is not a “thing” either – it is a determining principle. Only together do they produce a single, actual entity.

As Aristotle argues in Metaphysics H.6, the potential and the actual are in a sense one. The form is the cause of a substance’s unity and being. There is no separate explanation needed for why matter and form are one – their very natures are oriented toward each other.

Material and formal causes in the transformation of beings 🔗

The framework of material and formal causation provides a powerful tool for understanding how beings come into existence, persist, and transform.

Generation and corruption 🔗

When a new substance comes into being – for example, when chemical elements combine to form water – this is called generation. The matter (hydrogen and oxygen) receives a new substantial form (the form of water). The reverse process, corruption, occurs when a substance loses its form and its matter becomes available for new determination. A dead animal’s body decomposes; the matter that once constituted the animal is now informed by different forms – those of the simpler substances into which it breaks down.

In both cases, the material cause ensures that something persists through the change (matter never simply vanishes), while the formal cause determines the nature of what emerges. This explanatory structure avoids two extremes: it denies that things come from nothing (since matter always underlies change), and it denies that change is mere illusion (since real transformations of form genuinely occur).

Application to living beings 🔗

The relationship between material and formal causes is especially significant in the case of living organisms. For Aristotle and Aquinas, the soul is the substantial form of a living body. The soul is not a separate substance trapped inside a body – it is the organising principle that makes biological matter into a living thing. The body is the matter; the soul is the form. Together, they constitute a single living organism.

This has important implications. The form (soul) is responsible for the organism’s characteristic activities – growth in plants, sensation in animals, rational thought in humans. The matter (body) provides the substratum through which these activities are exercised. Neither can function without the other in the natural world. A body without a soul is, as Aristotle puts it, a body only in name – a corpse is not truly a human body, because it lacks the form that made it one.

The enduring significance of material and formal causes 🔗

The distinction between material and formal causes may seem like an ancient philosophical exercise, but it addresses questions that remain relevant. Modern science continues to grapple with the relationship between a thing’s composition and its structure. The question of whether DNA (a material component) or the organism’s developmental plan (a formal principle) is more fundamental to understanding life echoes the Aristotelian debate in a new key.

Philosophers working in the tradition of hylomorphism have argued that this framework avoids the reductionism of purely materialist accounts – which try to explain everything by reference to matter alone – and the abstractness of purely formalist accounts, which neglect the material conditions necessary for anything to exist. The strength of Aristotle’s approach is that it holds both principles together, recognising that being requires both something to be determined (matter) and something that determines (form).

What do you think? Can everything about a thing be explained by what it is made of, or does the organising principle – the form – add something that matter alone cannot account for? And in an age of artificial intelligence and synthetic biology, does the ancient distinction between material and formal causes still help us understand what it means for something to truly be?

References

1. https://plato.stanford.edu/entries/aristotle-causality/
2. https://aquinas101.thomisticinstitute.org/articles/selection-from-st-thomas-aquinas-on-the-principles-of-nature-cc-18-21
3. https://plato.stanford.edu/entries/form-matter/
4. https://www.britannica.com/topic/hylomorphism
5. https://www.saet.ac.uk/Christianity/Causality
6. https://aquinasonline.com/formal-cause/
7. https://plato.stanford.edu/entries/aquinas/