Here’s a problem that I’ve wrestled with for years: do the material parts (not just at the level of prime matter) of a substance survive through substantial change? For example, suppose a bit of watery fluid is extracted from my eye and placed on a microscope slide. Call the bit of watery stuff W. When W was part of my eye, it was (plausibly) essentially a part of me (even, perhaps, essentially part of my eye). On the slide, it is no longer a part of me it all. It seems to be an inorganic substance. But then it seems that it is not W itself but a new watery thing, W*, that exists on the slide. Non-substance W has apparently been annihilated and replaced by a new substance W*. The two things are physically and chemically indistinguishable.
This seems hard to believe. It’s even harder to sustain if we assume (as hylomorphists generally do) that a substance’s accidents belong essentially to that very substance. I.e., that individual substances also fail to survive through substantial change. So, the individual accidents of W* (its volume, mass, temperature, chemical composition, and so on) are all numerically distinct from the corresponding accidents of W. This raises the problem much discussed by late scholastic philosophers: the brown cow/brown carcass problem. If the substances making up the carcass are all numerically distinct from any substance existing before the cow’s death, then all of the accidents of parts of the carcass (like the brownness of the hide) are distinct from corresponding accidents (the brownness of the hide of the living cow) of the original substance. This introduces what seems an unnecessary complication to the story. It seems that we shouldn’t have to appeal to some special features of the cow or of the agent of the cow’s death to explain why the color of the hide is unchanged. The stability of the color should be the default expectation, based on our presumption that one and the same accident of color has persisted, since no agent has acted in a color-changing way.
There are two assumptions that lead to this impasse: the material parts of a substance are essentially parts of that substance, and the individual accidents of a substance are essentially accidents of that substance. Why not give up both assumptions? Let’s take them in order.
The main obstacle to giving up the first assumption is Aristotle’s No Substance in a Substance (NSIS) principle. Aristotle repeatedly asserts that no substance can contain another substance as a (proper) part. Many scholastic philosophers, including Scotus and Ockham, give up NSIS for this very reason. However, giving up NSIS undermines the per se unity of a material substance, turning such substances into mere heaps of their equally substantial components. So, can’t we keep NSIS while allowing material parts to survive substantial change?
Doing so seems to defy another very plausible principle: the Essentiality of Categorical Status (ECS). By ECS, I mean a principle that asserts that no substance can become a non-substance, and no non-substance can become a substance. To return to my example, W is a non-substance, so it cannot be identical to the substance W*.
However, there is a ready solution at hand, if we are willing to rely on the constitution relation that I introduced in an earlier post. We can say that W constitutes W* but is not identical to it. So, W survives the substantial change, not by becoming the new substance but by constituting it.
Let’s turn now to the second issue: the persistence of accidents. The key assumption here is that accidents are essentially tied to the substances that bear them. This seems to be true of what we could call formal or holistic accidents, like my feeling pain or activity of running. However, some accidents seem to belong most properly to some material part of the substance. These accidents are distributive: when part P has some accident A, every proper part of P also has A or some other accident A’ which is a determinate of the same determinable. Such ‘material’ accidents include things like chemical composition, temperature, phase of matter, color, mass, and volume. Why can’t we say that material accidents are essentially accidents of some material component of the substance? For example, we could say that the accident of brownness is essentially an accident of the cow’s hide (or, more precisely, the material thing that constitutes the cow’s hide). Now we can say that this hide-constituting part H survives the cow’s death. After the death, H constitutes an inorganic substance that is part of the cow’s carcass. Since H survives, there is no reason to deny that H’s accident of brownness also survives.
As the example illustrates, there are some material parts of the cow that do not survive death: the hide, the eyes, the stomach, and so on. We can call these the integral parts of the cow. These are the things that Aristotle’s Homonymy Principle applies to: after death, the cow’s “eyes” are no longer really eyes. So, the cow’s eyes do not in fact survive. However, there are other material parts of the cow that do survive. In particular, there is a material part L that constitutes the cow’s left eye, and this part can survive death by later constituting some inorganic substance.
The Analytic Thomist 