Individuating substances by their matter

According to traditional Aristotelianism, what makes you and me be distinct entities is that although we are of the same species, we’re made of distinct chunks of matter.

Here is a quick initial problem with this. The matter in us changes. It is quite possible that someone has different matter at age 1 and at age 20, and so by the Aristotelian individuation criterion, they are a different entity of the same species at ages 1 and 20, which is false.

One way out of this is to embrace presentism. But presentism is incompatible with the Aristotelian conviction that truth supervenes on being.

Another move is to narrow down the individuation criterion to say that:

1. Conspecifics x and y are made distinct by their being simultaneously made of different chunks of matter.

There are two problems with this move.

First, time travel. If at age 20, with different matter, you enter a time machine and travel back to meet yourself back when you were 1, then 20-year-old you and 1-year-old you are made of different chunks of matter at the same time. And while many problems about time travel are solved by moving from external to internal time, that doesn’t work here. For one cannot say that matter individuates x and y at the same internal time, since internal time is a concept that only makes sense when you are dealing with a single substance.

Second, relativity theory and teleportation (which is also kind of like time travel). Suppose that by age 20 you have different matter from what you had at age 1. Then God teleports 20-year-old you 100 light-years away instantly or nearly instantly (with respect to some reference frame). Then there will be a reference frame with respect to which it is true that the teleported 20-year-old you is simultaneous with 1-year-old you. So either simultaneity with respect to that reference frame doesn’t count—and that leads us to a privileged reference frame, contrary at least to the spirit of relativity—or else you are not yourself, which is absurd.

While one can swallow the idea that time travel is impossible, spacelike teleportation seems clearly possible.

Here is another move: we replace (1) with:

2. Conspecifics x and y are made distinct by their originating in distinct chunks of matter.

And 20-year-old you, no matter how they travel in space and/or time, has originated in the same chunk of matter as 1-year-old you.

This move has a cost: it requires that we be somewhat non-realist about substantial change. Full-blown realism about substantial change requires the matter to stay in existence while the substance changes. But if matter can stay in existence when its substance perishes, then that matter could be re-formed into another substance of the same species, which would violate the origination-restricted indviduation criterion. On (2), we have to accept the theory that the matter of a thing perishes when the substance does. This removes one of the major motivations behind positing matter: namely, that matter is supposed to explain why a corpse looks like the living body (viz., because it is allegedly made of the same matter).

Note, too, that (2) has a serious ambiguity once we have insisted that matter does not survive substantial change. By the chunk of matter that a substance originates in, do we mean the last chunk of matter before the substance’s existence or the first chunk of matter in the substance?

If we mean the last chunk of matter before the substance’s existence, there are two problems. First, it seems ad hoc to single out one aspect of the causes of the substance—the earlier matter—as doing the individuating. It seems better to individuate by means of the causes, applying the converse of the essentiality of origins. Second, it seems possible for an object to come into existence without prior matter. (If God exists, this is clear, since God creates ex nihilo. If God doesn’t exist, then very likely the world came into existence ex nihilo.) But then it seems quite possible for two objects of the same species to come into existence without prior matter. (Though if one wants to dispute this, one might point to the fact that a literal reading of the biblical creation account has God making the first two humans out of chunks of preexisting matter—soil and rib respectively. Maybe there is a deep metaphysical reason why this has to be so, and perhaps the initial ex nihilo created things had to be all of different species. But I just don’t find the latter requirement that plausible.)

So perhaps in (2) we mean the first chunk of matter in the substance. But if matter does not survive substantial change, then it seems plausible that the identity of the substance is prior to the identity of its initial matter, and hence the identity of the substance cannot come from its initial matter. This isn’t a very strong argument. Maybe the initial matter is prior to the substance, and has an identity of its own, while later matter is posterior to the substance.

So, our best version of the Aristotelian individuation account is this:

3. Conspecifics x and y are made distinct by their each having a different first chunk of matter.

Finally, it is interesting to note that (2) and (3) are only plausible if it is impossible for a material substance to have no beginning. But our best account for why a material substance cannot have a beginning is causal finitism. So those who like the Aristotelian account of individuation—I am not one of them—have another reason to accept causal finitism.