Hylomorphism – Wikipedia
In some cases, a substance’s matter will itself be a substance. ... According to Aristotelians, such a substance has only “prime matter” as its matter. Prime matter is matter with no substantial form of its own. Thus, it can change into various kinds of substances without remaining any kind of substance all the time.

Hope this helps.

I think water would be a good example of prime matter.

Earth, air, fire and water are the prime matters in philosophy in the past.

@Dutchess_III @RedDeerGuy1 Earth, water, air, and fire are elements. They cannot be prime matter because the whole point of the prime matter hypothesis was to explain the underlying nature of elements and how they can change despite being otherwise fundamental.

@thywater Prime matter is something that Aristotle’s interpreters (such as Augustine and Aquinas) attributed to him in order to solve an apparent problem with his theory of matter and change. According to Aristotle, everything is made out of the four elements: earth, water, air, and fire. Furthermore, each element is either hot or cold and either wet or dry (earth is cold and dry, water is cold and wet, air is hot and wet, fire is hot and dry). One of the ways that an object undergoes change is for the elements that make it up to exchange one set of properties for another. So water can become air by going from cold to hot, and it can become earth by going from wet to dry.

But wait! If the elements can change into one another, then there must be something underlying them that undergoes this change. That is, there must be something that goes from being cold and wet to being hot and wet. It can’t be the water itself, because water is always cold and wet. Water cannot become hot and wet because being water just is being cold and wet. The underlying thing that holds these properties is the so-called “prime matter.” Prime matter does not itself have any essential properties. It is, in Aristotle’s terms, pure potentiality (it can be anything, but there is nothing that it must be). When prime matter is cold and dry, it is earth. When it becomes cold and wet, it is water. When it becomes hot and wet, it is air. And when it becomes hot and dry, it is fire.

Obviously, this whole idea predates modern atomic theory. It’s also worth noting that “earth” doesn’t mean “dirt” on Aristotle’s view, and water doesn’t mean H₂O. In fact, the four classical elements are more closely related to the modern states of matter (where earth = solid, water = liquid, air = gas, and fire = plasma, though classical fire might be closer to pure energy than it is to plasma).

@SavoirFaire Right. Sorry I got confused with the Prime Material Plane from D&D.

Prime Material Plane from D&D

I just got confused in general. My first reaction was 1, 2, 3, 7, 13….

Common to all things that don’t have an essence, a nature, is the matter that that essence is joined to. Think of a human being who just died. He is the matter but not human. Now think of every physical thing in the world and what must be common to all BEFORE they get their differentiation by essence. Look up “Hylopmorphism”—I have a bunch of good books on the topic