Everyone from the Pre-Socratics to the guy writing Chemistry textbooks agrees that matter is what things are made of or what changes from one thing to another, but Aristotle’s unique discovery is that what changes cannot be fixed, definite, or actual.

When the bird on an elm flies to a maple neither the bird as bird nor the bird as on elm is what changes. As bird it stays the same, and being-on-an-elm never becomes being-on-a-maple. To allow for what changes Aristotle was compelled to admit a reality that was not itself definite or actual or with any logos as all. Of course we need not compel ourselves to this but can just take motion as a given and analyze it into subatomic particles, but matter as such – even what the chem. textbook means by matter – remains a reality neither definite, fixed, actual or with a logos in itself.

What changes depends on definite, actual logoi without itself being a definite actual logos. The dependence is continual: at any moment in the bird’s flight we can freeze the motion, at least in thought, and the bird will have just as definite a place as it had at the beginning. In Chemistry or particle physics we treat these continually present definite and actual logoi on which matter depends.

What changes depends not just on definite features but also on the end. This is why actions can be frustrated or done in vain, like driving to a store that is closed or a mouse seeking to feed on the peanut butter on the trap. Purely inertial, mechanical or natural motions move only instrumentally and so considered in themselves are infinite in both directions. Their end is whatever end is given to them by a principal agent, and their nature is whatever ends-from-another they are capable of maintaining.*

Matter therefore is not definite or actual in two ways. On the one hand as a subject composing things and as as a natural being which is nothing but an openness to the activity of some principal, living agent. This is just as true of subatomic particles and virtual fields as of earth, air, fire and water.

*We can define nature as the way in which anything is capable of executing the action of a principal agent. Insight into nature in a living being is an insight into what use life makes of nature, insight into the universe as a whole is an insight into what God and the angels are performing outside of themselves.

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