On Physics

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A body is defined by the ancients in this way: A body is everything that has three dimensions, namely: Length, width, and depth. Or, defined better according to Algazel Al-Ghazali, a Persian theologian and philosopher and Avicenna Ibn Sina, a highly influential Islamic physician and philosopher: A body is that in which there is a capacity for perceiving two lines intersecting each other at right angles, and a third line intersecting both of those at right angles.

Furthermore, of bodies, one type is mobile and the other immobile. And I call an immobile body a standing body that does not move, neither in regard to its position nor its form, such as that which is called the empyrean heaven The highest part of the medieval cosmos, believed to be the abode of God and the angels, composed of pure light or fire. A mobile body, however, is that which is subject to motion and rest; this is also one of the principles of natural science, according to the testimony of Aristotle at the beginning of the first book of the Physics.

According to the testimony of the same Aristotle, there are three principles of nature: namely, the subject (or matter) and two contraries, namely, privation The absence of a quality or form that should naturally be present and form. This can be shown as follows: in everything that comes to be according to nature, it is necessary that something be the subject for that which is coming into being in potentiality. By saying "something be the subject," I touch upon matter, or the subject. By saying "that which comes to be," I touch upon form. By saying "in potentiality," I touch upon privation.

For example: From a non-musical man, a musical man is made. From a seed that is not a man, a man is made. Therefore, matter is one principle in number, and it is as if it were two by reason of privation; for privation happens to matter. For it is not the same thing for a man to be, and for a "non-musical thing" to be. Because, as Aristotle says, there are two primary principles, if one speaks in terms of number. Yet they are not entirely two, because of that which "being" is to them, but rather three.

That matter and form are the principles of any body is evident through resolution The logical process of breaking a thing down into its simplest components: for when all accidental forms are abstracted, one finally arrives at the substantial form; when this is still abstracted by the intellect, there remains something deeply hidden, which is "prime matter" The most basic, formless reality that underlies all physical things. That this matter is indeed something is evident from the fact that the elements mix with one another, and not according to their contrary qualities or forms; for according to those they are repugnant to each other. Therefore, according to something else, there is something common to all of them, which is prime matter; therefore prime matter is something.

And if it is objected that "all being comes from form," and therefore if this matter is something it must have a form (and thus would not be prime matter), it must be said that actual being comes from form, but not potential being; and prime matter has such potential being. Or it can be said that the capacity for receiving every form serves as its form. For Aristotle says in the first book of the Physics: "We think we know each thing when we know its first causes and first principles, down to the elements." Therefore, we must speak of these principles individually, and first concerning matter.

On Matter. Chapter 3.

Matter, as Aristotle says at the end of the first book of the Physics, is the primary subject for each thing, out of which something is made while it [the matter] persists, and not by accident. He says "while it persists" because in everything that is made according to nature...