Interestingly enough, the Thomist agrees, in principle, with at least one claim of the Naturalist. In this sense, Thomism is a Christian Naturalism. The Thomist would agree that matter is a basic, substantial, principle of all sensible, material, entities. We saw in a previous post that, for the hylomorphist, matter is one of two principles out of which all material, sensible, things are composed. Though the Naturalist attempts to claim that matter is atoms, or, whatever the natural sciences claim is most basic, the Thomist recognizes that these descriptions do not define what matter is. Rather, an atom, or, whatever seems to be most basic according to the natural sciences at any given time, is simply another form of matter; and this way of explaining it leads us into the Thomistic explanation of matter.
In his short treatise De Principiis Naturae Aquinas explains what he considers to be the basic principles from which all material things spring. He begins by pointing out what seems to be a platitude, “Take note that some things can exist, though they do not, whereas others do indeed exist. Those which can exist are said to be potentially. Those which already do exist are said to be actually.” Aquinas then goes on to explain that, of those things which actually exist, some exist substantially, and others exist only accidentally. Accidental existence is found in a subject, whereas substantial existence describes the thing itself, its essence.
Earlier we noted that one of the problems with Naturalism is that in attempting to define matter it gives us a list of characteristics, in other words, accidents. Bobik, in his commentary on Aquinas’ De Principiis Naturae, notes that “The ultimate existing subject is I - - this rational animal. My being five feet eight inches tall, and white, and knowledgeable, etc. - - no one of these is what I am as an ultimate existing subject. Neither is the collection of them what I am as an ultimate existing subject. Furthermore, no one of them, nor the collection of them, is itself an ultimate existing subject.”
If we apply what we have just seen to the claims of Naturalism, we find that the Naturalist is attempting to say that some substantial entity is the foundation of reality. But we want to know what matter is. Even the most basic substantial entity, be it the atom, or energy, or anything else, is still composed, as we shall see, of matter and form.
Aquinas goes on to describe what he has already alluded to when he talked about things that exist, do not exist, and potentially exist. “Both what is in potency to substantial existence, and what is in potency to accidental existence, can be called matter…But they differ in this: the matter which is in potency to substantial existence is called the matter out of which; and that which is in potency to accidental existence is called the matter in which. Properly speaking, however, what is in potency to substantial existence is called prime matter; whereas what is in potency to accidental existence is called a subject.”
Prime matter is pure potency, having no existence by itself. A subject, however, is not pure potency, but is in potency to certain accidents. For example, a child, which is a subject, is in potency to become an adult. Unfortunately, as we all too frequently find out, a child also has the potency to become an inanimate body. When this happens we are always pained, and rightly outraged, but the potency is there from the moment that the child’s form is in act. In order to fully understand pure potency, it needs to be explained in light of form; due to the fact that pure potency is formless, it is only that which can be.
“Now just as everything which is in potency can be called matter, so too everything from which something has existence, whether substantial or accidental, can be called form.” Form is that principle which limits matter – potency. Matter is that principle which, makes the form, this individual; it is the principle of individuation. “First matter, the indeterminate but determinable principle which makes possible the transformation of one substance into another; and first form, the determining principle which accounts for the fact that a given substance is the particular thing that it is and not something else [meaning it’s essence]…If first matter represents what a thing can be, first form represents what a thing is.”
Matter, then, in the Thomistic perspective, is that principle of potency which individuates form - that is, which makes a human person to be this human person (i. e. - Socrates). But matter cannot exist by itself. Without form there can be nothing. This becomes clear when we try to imagine, or think about, or point to, a particular blob of pure matter. It cannot be done. Matter always exists united with form in some way or another. “First matter is separable from first form in thought, though never in fact. There is no such thing as first matter without first form…First matter has no character in itself. It is absolutely featureless, formless, and indefinite, without quality, without quantity. To acquire definiteness and quality, to be earmarked with quantity, it must have first form. It is potentially everything, though it is actually nothing.” As such, matter is not some single substance; rather the most basic substances are subjects that are composed of matter and form, and are potentially other things.
Joseph Bobik, Aquinas on Matter and Form and the Elements (1998; repr., Notre Dame, IN: University of Notre Dame Press, 2006), 1.
Robert Edward Brennan, Thomistic Psychology: a Philosophical Analysis of the Nature of Man (1941; repr., New York: The Macmillan Company, 1946), 66-67.